Keys to genera of Thai Rubiaceae [1]


Excludes ornamentals and crop plants [For these see Key to cultivated taxa and Cultivated Rubiaceae]

– An asterisk (*) following a genus name means that a genus either is monotypic or that it is represented by only one (a single) species in Thailand.


1. Epiphytic plants


1*. Terrestrial plants (although some herbs occasionally also epiphytic on tree trunks)


2. Epiphytes with large, conspicuous ant-inhabited tubers


2*. Epiphytic (or hemi-epiphytic) woody plants without tubers


3. Tubers unarmed; leaves to 9 cm long, elliptic to elliptic-oblong or obovate


3*. Tubers with short thorns; leaves at least 10 cm long, elliptic


4. Epiphytic strangler with Ficus-like habit; leaf blades auriculate at base


4*. Epiphytic shrubs, not strangling (see Note 1, below); leaf blade bases never auriculate


5. At least some of the stems with adhesive adventitious roots along the internodes; flowers in globose heads; ovaries and fruits of a head tightly pressed together but not fused; individual fruitlets berry-like, many minute seeded


5*. Stems without adventitious roots along the internodes; inflorescences not as above; fruits capsular, with many large, elongated winged seeds


6. Inflorescences erect, consisting of several c. 2-7-flowered partial inflorescences, each of these subtended by a white to creamy white show bract; flowers large (corolla tubes 30-55 mm long)


6*. Inflorescences pendulous, typically consisting of 2 simple, raceme-like units arising at one point; each unit with a solitary, outward-pointing, long-petiolate pale green to greenish-white leaf-like bract; flowers minute (corolla tubes c. 2 mm long)

 Hymenodictyon p.p. [H. flaccidum]

7. Plants with globose flowerings heads or with flowers collected in head-like aggregates [see Note 2 below]


7*. Inflorescences not as above 


8. Herbaceous plants (including shrubby herbs and shrublets; see Note 3, below)


8*. Woody plants


9. Woody plants with thorns or hooked thorns (hooks)


9*. Woody plants without thorns or hooks


10. Woody plants with colored (often white, creamy white or greenish white) showy leaf-like structures in the inflorescence region (usually still present in fruiting stage but then no longer colored and thin and papery)


10*. Woody plants without such structures


11. Woody climbers  (lianas) and straggling or scandent shrubs (see NOTE 4, below)


11*. Trees, treelets and shrubs [including some indistinctly straggling and scandent shrubs, and including subshrubs (see Note 3, below)]




Note 1.– If you are uncertain about the epiphytic habit, continue at couplet 6 (taxa in question will be keyed out again).


Note 2.Globose flowering heads: numerous sessile, subsessile or pedicellate flowers on a common globose axis (receptacle), with or without interfloral bracteoles; adjacent ovaries of sessile flowers sometimes united by tissue fusion. – Flowers in head-like aggregates: (much) congested thyrsic inflorescences, with inflorescence branches recognizable (but extremely shortened; flowers thus not inserted on a common globose receptacle. – If you are not certain about this character, use either the herbaceous plants key (KEY B) or the woody plants keys (KEY C, KEY E, KEY F).

Note 3.– Definitions: Shrubby herbs and shrublets are defined as essentially herbaceous plants whose stems are usually somewhat woody at the base (but ± massive woody underground parts are absent); they are keyed out in KEY B. Subshrubs, in contrast, are essentially shrubs whose woody body is mostly underground; they are keyed out in KEY F.

Note 4. – Only clearly and distinctly straggling or scandent shrubs are included here. If you are not certain, use KEY F.



KEY A. Key to taxa with globose heads or head-like flower aggregates

[see Note 1, above, for definitions]


1. Globose flowering heads; trees, shrubs or climbers (rarely treelets or geoxylic suffrutices: Morinda p.p.!)


1*. Flowers in head-like aggregates; mostly herbs, occasionally subshrubs, shrublets or shrubby herbs, sometimes climbing [if trees or shrubs with +/- head-like inflorescences, use KEY F!]


2. Climbing shrubs, sometimes epiphytic climbers


2*. Trees or shrubs, rarely treelets or geoxylic suffrutices, non-epiphytic


3. Plagiotropic branches with paired hooks; flowering heads with pedicellate, subsessile or sessile flowers


3*. Plants without hooks


4. Epiphytic climbing shrubs with adhesive climbing roots; flowering head relatively large, neighboring ovaries in close contact with each other but not fused; fruiting head consisting of closely spaced (but not fused) many-seeded berry-like fruitlets


4*. Non-epiphytic climber; flowering heads small, neighboring ovaries fused; fruiting heads small consisting of fused fruitlets, each with 2 pyrenes

 Morinda p.p. [M. umbellata]

5. Ovaries of all flowers of a head fused, in fruit a fleshy syncarp of fused drupes [except in 1 species where ovaries and fruits are in close contact only but not fused]; heads solitary, stalked, mostly opposite a solitary leaf (leaf-opposed); flowers heterostylous 

Morinda p.p.

5*. Plants not with the above combination of characters


6. Stipules bifid, divided almost to base, loosely surrounding terminal bud; flowering heads small (to c. 1 cm across corollas)


6*. Stipules not divided; flowering heads small to large


7. Flowers consistently 4-merous; ovaries with 2 ovules (1 per locule); fruitlets 2- (or, by abortion, 1-)seeded, hard, indehiscent; fruiting heads an aggregation of loose individual fruitlets


7*. Flowers predominantly 5-merous; ovaries multiovulate; fruitlets many-seeded and mostly dehiscent (then seeds winged), seldom fruitlets indehiscent and ± fleshy (then seeds unwinged); fruiting heads mostly an aggregation of loose individual fruitlets, seldom fruitlets united into an indehiscent syncarp


8. Stipules large and broad and with obtuse-rounded apex, in vegetative buds (at tips of branches) flattened and ± tongue-shaped


8*. Stipules narrow and pointed, in vegetative buds (at tips of branches) clasping and conical to pyramidal in shape and not conspicuously flattened


9. Inflorescences consisting of a cluster of 2–4(-10) stalked flowering heads arising in the axils of foliage leaves


9*. Inflorescences not as above, typically terminal but also terminal and/or axillary


10. Flowers of a flowering head united by their ovaries; fruitlets of a head united into an indehiscent syncarp; seeds unwinged; young heads not surrounded by involucre-like stipules or bracts


10*. Flowers of a flowering head closely spaced but not fused by their ovaries; fruitlets of a fruiting head free from one another but closely spaced, individual fruitless capsular, seeds winged; young heads subtended by a pair of (small) leaves with enlarged, sometimes somewhat colored deciduous stipules, or only the involucre-like enlarged stipules


11. Inflorescences consisting of 1-3 flowering heads; calyx lobes differentiated into a narrow, basal persistent part (“shaft”) and an expanded (often spathulate to clavate) apical portion which comes off soon and is only seen in bud; style with subglobose stigma


11*. Inflorescences often extensive, frequently 10 or more flowering heads in thyrse- to pseudo-umbel-like arrangement; calyx lobes not differentiated as above, the entire calyx lobes persistent; style with mitriform to elongate, clavate stigma


12. Inflorescences consisting of at least 7 flowering heads, often in simple thyrse-like arrangement


12*. Inflorescences solitary, pedunculate flowering heads, or with only up to 3 flowering heads


13. Stipules 2-4 mm long; flowering heads 6–12 mm in diam. across corollas; fruiting heads 6-10 mm in diam.


13*. Stipules 10-15 mm long; flowering heads 15–20 mm in diam. across corollas; fruiting heads 10-15 mm in diam.


14. Inflorescences axillary, usually consisting of solitary, pedunculate, small flowering heads (< 10 mm in diam. across corollas


14*. Inflorescences terminal, consisting of solitary, pedunculate, large flowering heads (at least 30 mm in diam. across corollas


15. Fruiting head an aggregation of tightly packed but not fused individual fruitlets, the latter slightly fleshy and indehiscent, with minute, unwinged seeds; calyx lobes 2-2.5 mm long


15*. Fruitlets of a fruiting head partially cohering, eventually breaking apart into semi-free cocci, seeds shortly winged on both sides; calyx lobes 4-5 mm long


16. Shrubby herb or shrublet with large leaves (15-28 cm long) and stipules (1-2 cm long); inflorescence a terminal, pedunculate, compact, many-flowered head subtended by small, involucre-like bracts; flowers small, 5-merous; calyx lobes as long as or longer than corolla tube, resembling interfloral bracts


16*. Not with the above combination of characters


17. Climbing herbs (sometimes ± woody at base)

 Hedyotis p.p. [H. capitellata, etc.]

17*. Not climbing


18. Inflorescence thyrso-paniculate, the partial inflorescences congested and forming globose head-like aggregates; corolla lobes uncinate at apex; fruits consisting of 2 1-seeded mericarps splitting from the base upwards, leaving behind the carpophore

Knoxia p.p. [forms of K. roxburghii]

18*. Inflorescence not as above; corolla lobes not uncinate at apex; fruits capsular (rarely drupe-like, modified capsules)


19. Entire inflorescence a single pedunculate or sessile head

Hedyotis p.p. [H. oligocephala, H. cornonaria, etc.]

19*. Flowers forming globose aggregations in leaf axils (or sometimes leafless nodes) and often also terminal on stems


20. Fruit a 2-seeded circumsessile capsule with the upper half plus persistent calyx lobes coming off; erect or spreading annual herb with minute flowers in axillary and terminal heads


20*. Fruit a 2-valved capsule (or sometimes a modified, indehiscent drupe-like capsule)


21. Capsule with a single, elongated seed in each locule

 Spermacoce p.p.

21*. Capsule many- to several seeded, uncommonly indehiscent, drupe-like (H. philippinensis, etc.!)

Hedyotis p.p.



KEY B. Key to herbaceous taxa

[including “shrubby herbs” and “shrublets.” See Note 1, above, for definitions. If you are not certain about this character, try KEY F]


1. Shrubby herbs or shrublets, often unbranched, with relatively large elliptic to oblanceolate leaves (c. 8-30 cm long and 3-8 cm wide)


1*. Plants distinctly herbaceous (if approaching shrublets then with much smaller leaves than above)


2. Flowers pendulous, relatively large (tube c. 15 mm long), pedicellate, in quite loose 5-20-flowered inflorescences; stamens with flattened, united filaments and anthers united into a cone; ovary long (7-9 mm) and narrow; fruit elongated, cylindrical, c. 25-30 mm long


2*. Flowers minute (corolla < 5 mm long); inflorescences consisting of several helicoid/scorpioid cymes radiating out from the centre in a star-like fashion; each arm on the upper side with 4 rows of flowers united by their ovaries; stamens free; ovary to 2 mm long; fruits minute, united into a slightly fleshy “syncarp” 


3. Leaves and leaf-like stipules forming pseudo-whorls of 4-6 


3*. Leaves opposite (decussate), never with leaves and leaf-like stipules forming pseudo-whorls (but sometimes appearing whorled because of much-contracted internodes: Argostemma)


4. Leaves (sub)sessile in pseudo-whorls of 4 or 6, 1-or 3-nerved; flowers 4-merous; fruits dry, breaking into 2 single-seeded mericarps


4*. Leaves usually distinctly petiolate, in pseudo-whorls of 4, mostly 3- or 5-nerved; flowers typically 5-merous; fruits consisting of 2 fleshy, single-seeded mericarps

 Rubia [except R. siamensis]

5. Plants forming mats or low cushions or at least creeping; stems often with adventitious roots


5*. Growth form not as above


6. Creeping, often rooting stems (usually covered in sand) producing short, erect flowering/fruiting side shoots with several closely spaced leafy nodes; leaves imbricate, narrowly elliptic(-oblong) or spathulate, subsessile, succulent; flowers/fruits usually solitary in leaf axils (ovaries/base of fruits at least partly hidden in stipular sheath); fruit indehiscent, corky, longitudinally ribbed and laterally compressed, with 2 (or, by abortion, only 1) seeds; plants confined to sandy coastal areas


6*. Not as above


7. Fruits red, orange-red or orange drupes with two 1-seeded pyrenes


7*. Fruits dry, typically capsular, sometimes modified indehiscent capsules or capsules eventually splitting into 3-4 1-seeded cocci


8. Creeping, often rooting stems producing short, erect to ascending flowering/fruiting side shoots with few or only 1 pair of petiolate, orbicular to reniform and cordate leaves; inflorescence few- to 1-flowered, terminal on leafy shoots; flowers 5(6)-merous, corolla pure white, relatively large (tube plus corolla at least 12 mm long), stamens and stigmas included


8*. Much-branched prostrate and mat-forming herbs; shoots not differentiated as above; leaves elliptic to broadly ovate; flowers solitary, terminal 4-merous, corolla greenish to greenish-white, small (tube plus lobes to c. 2.5 mm long), stamens and long stigmas conspicuously exserted


9. Creeping, much-branched herbs, often forming dense mats or cushions; flowers singly in leaf axils at alternate nodes or terminal in branch forks; fruit a many-seeded, indehiscent modified capsule


9*. Plants usually not forming dense mats or cushions; flower arrangement not as above; fruits usually (but not always: Neanotis spp.!) dehiscent 


10. Fruit capsular, eventually splitting into 3-4 cocci, each coccus with a solitary, ventrally grooved seed; flowers with 3-4 stigma lobes


10*. Fruit capsular but not splitting into cocci; flowers with 2 stigma lobes


11. Fruit a 2-valved capsule with a single, elongated, ventrally grooved seed in each locule; flowers in densely clusters in leaf axils and often also terminal

Spermacoce p.p.

11*. Capsules with typically with many to several seeds (if few seeds or, rarely, a single seed, seeds neither elongated nor grooved)


12. Plants foetid when bruised; fruits capsular, dehiscing at the apex only or remaining indehiscent, with few seeds

Neanotis p.p.

12*. Plants not foetid; fruits capsular, dehiscent, many- to several-seeded

Hedyotis/Oldenlandia p.p.

13. Fruits consisting of 2 fleshy, globose, single-seeded mericarps; climbing herbs with 4-angled stems scabrous at the angles; inflorescence many-flowered, flowers campanulate, c. 3 mm across

Rubia p.p. [R. siamensis only]

13*. Plants not with the above combination of characters


14. Vegetative part of plant reduced, with a large, seemingly solitary basal leaf (actually an extremely anisophyllous leaf pair, with the small leaf of a pair hardly discernible) and with or without another 1 or 2 pairs of isophyllous or ± anisophyllous leaves 


14*. Not as above


15. Flowers with an infundibular corolla, tube to 12 mm long


15*. Flowers distinctly Solanum-like (corolla star-like, tube almost completely reduced)

 Argostemma p.p.

16. Flowers distinctly Solanum-like (corolla star-like, tube almost completely reduced)

 Argostemma p.p.

16*. Corolla not star-like


17. Corolla campanulate; fruits capsular, the flat top coming off like a lid, many-seeded

 Argostemma p.p.

17*. Corolla typically infundibular (if corolla subcampanulate then fruits drupaceous); fruit typically not a lid-capsule (if so, a 2-seeded circumsessile capsule with the upper half plus persistent calyx lobes coming off) 


18. Flowers and fruits sessile, in terminal, pedunculate, erect, spike-like helicoid/scorpioid cymes; ascending low herb


18*. Plants not with the above combination of characters


19. Plants with a basal rosette of 2 or more leaf pairs, leaves flat on the ground


19*. Basal leaf rosette absent


20. Corolla 4-merous, lobes uncinate at apex; calyx lobes unequal; fruits splitting into 2 mericarps from the base upward, leaving behind a carpophore; 1 seed per mericarp

Knoxia p.p. [K. rosettifolia only]

20*. Corolla 4- to 5-merous, lobes not  uncinate at apex; calyx lobes equal; fruits capsular, many- to several-seeded

Hedyotis p.p.

21. Fruit fleshy ( i.e. a didymous drupe breaking into 2 one-seeded mericarps), minute (c. 1.5-2 mm in diam.); inflorescences on recurved, hairy peduncles, made up of typically 5 partial inflorescences (each dense, compact at anthesis, but elongating to 15 mm during fruit maturation)


21*. Fruit dry; inflorescences not as above


22. Fruit a 2-seeded circumsessile capsule with the upper half plus persistent calyx lobes coming off; erect or spreading annual herb with minute flowers in axillary and terminal heads


22*. Fruit never a lid capsule, dehiscent or tardily dehiscent, rarely indehiscent


23. Fruits with 1 seed per locule (ovary locule with a solitary ovule)


23*. Fruits many- to several-seeded


24. Inflorescences terminal (or terminal and axillary), thyrso-paniculate, lax and corymbose, variously congested or head-like; flowers heterostylous; corolla lobes uncinate at apex; fruits dehiscent to tardily dehiscent into 2 one-seeded mericarps, leaving behind variously shaped carpophores


24*. Flowers in clusters in foliage leaf axils and often also in the axil of terminal leaf pair; flowers isostylous; corolla lobes not uncinate at apex; fruits capsular, dehiscing septicidally from the apex downwards into 2 valves

 Spermacoce p.p.

25. Capsule obcordate, usually much broader than high, strongly laterally compressed, opening apically to reveal a narrow slit, seeds very numerous; inflorescences often consisting of scorpioid/helicoid cymes; flowers 5-merous


25*. Capsules typically (sub)globose, sometimes ± didymous, dehiscing loculicidally and/or septicidally, sometimes dehiscing at the apex only or remaining indehiscent altogether, seeds many to several, sometimes few; flowers 3- to 6-, usually 4-merous


26. Plants foetid when bruised; capsules dehiscing at the apex only or remaining indehiscent, with few seeds

Neanotis p.p.

26*. Plants not foetid; capsules dehiscent, sometimes conspicuous beaked (with the apex protruding),  many- to several-seeded




KEY C. Key to woody taxa with thorns or hooked thorns (hooks)


1. Curved thorns or hooks; plants straggling or climbing, never erect trees or shrubs


1*. Straight thorns; plants with erect main stems 


2. Inflorescences pedunculate, many-flowered, globose heads; stipules (in at least some species) bifid at apex 


2*. Inflorescences otherwise; stipules never bifid


3. Branches (long shoots) with abbreviated leafy and/or flowering shoots and thorns immediately above them (arising at the same node; accessory bud/shoot formation); flowers relatively small,  always less than 1 cm in diam., mostly greenish, greenish-white or greenish-yellowish,  in fascicles on very abbreviated shoots; fruits drupaceous

Canthium p.p.

3*. Branches (long shoots) with paired hooked thorns (leafy and/or flowering brachyblasts not present in the vicinity of thorns); inflorescences terminal, flowers relatively large, usually > 1 cm in diam., white; fruits berry-like


4. All hooked thorns on a branch of the same kind

Oxyceros p.p.

4*. Thorns pairs basal on lateral branches fang-like, larger and robust than hooked thorns at the following nodes

Oxyceros p.p.

5. Trees with branches bearing short lateral shoots which terminally produce one or two pairs of short, straight thorns 


5*. Arrangement of  thorns not as above 


6.  Thorns or thorn-tipped short lateral branches bearing very abbreviated leafy and/or flowering shoots 


6*. Thorns neither with leafy nor with flowering abbreviated shoots


7. Numerous pairs of thorns on often ± fascicled branches found in the lower part


of  trunk; branches of the crown mostly thorn-less; trunk and older branches typically rusty- to red-brown; flowers relatively large (to c. 2 cm in diam.), green, unisexual 


7*. Not as above; branches (long shoots) with abbreviated leafy and/or flowering shoots  and thorns immediately above them (arising at the same node; accessory bud/shoot formation); flowers either considerably smaller than above or, if relatively large, not green and not unisexual


8. Flowers relatively large, typically > 1 cm in  diam., mostly white (but turning yellow to orange with age in Catunaregam), in ± many- to few-flowered terminal inflorescences, or solitary flowers terminal on abbreviated shoots; fruits berry-like drupes, without distinct stones 


8*. Flowers relatively small,  always less than 1 cm in diam., mostly greenish, greenish-white or greenish-yellowish,  in fascicles on very abbreviated shoots; fruits typical drupes with 2-5 stones (pyrenes)


9. Thorns often long, to 4 cm;  flowers 5-10-merous, large (2 cm or more in diam.), solitary (or in groups of few), older corollas turning yellow to orange; fruits large, at least 2 cm long or in diam. 


9*. Thorns smaller, usually not more than 1 cm long; flowers 5-merous, smaller, usually in ± many- to few-flowered inflorescences, old flowers not turning conspicuously yellowish or orange; fruits small, often less than 1 cm in diam.


10. Thorns often long, to over 5 cm, sometimes both in whorls of 3 or opposite on the same individual; ovary 5-carpellate, drupes typically with 5 stones (sometimes fewer due to abortion) relatively large (to ca. 3 cm in diam.)


10*. Thorns typically much shorter (sometimes thin and inconspicuous and less than 1 cm long), opposite only; ovary2(-3)-carpellate, drupes with 2(-3) stones (or, due to arbortion, a solitary stone), normally smaller, mostly not more than 1 cm in diam.

Canthium p.p.



KEY D. Key to woody taxa with colored showy leaf-like structures in the inflorescence region


1. Colored, enlarged leaf-like bracts subtending partial inflorescences


1*. Some flowers of an inflorescence with stalked, leaf-like colored calyx lobes


2. Bracts greenish white or tinged pinkish, broad, subsessile, subtending much congested partial inflorescences, usually in several decussate pairs 

 Psychotria p.p. (“Cephaelis”)

2*. Bracts white, creamy white, greenish white or greenish, long-petiolate; inflorescences not much congested


3. Epiphytic (or sometimes terrestrial) shrubs; inflorescence consisting of several c. 2-7-flowered partial inflorescences, each of these subtended by a colored bract


3*. Deciduous trees; inflorescence elongated, raceme-like, at its base at least one outward-pointing bract


4. Usually climbing shrubs, rarely treelets; fruits indehiscent, fleshy, berry-like


4*. Small tree or treelet with decussate, spreading to ascending branches with terminal inflorescences; fruits dry, capsular




KEY E. Key to woody climbers (lianas) and straggling or scandent shrubs

[See Note 4, above]


1. Plants with mostly distinctly hooked thorns (hooks)


1*. Thorns or hooks absent


2. Inflorescences (several-flowered cymes) in leaf axils; flowers 4-merous


2*. Inflorescences not in leaf axils; flowers 4-7-merous


3. Inflorescence from a leaf-less node (or leaves at this node highly reduced and bract-like), separated from leaf-bearing node by a distinct internode (to 2.5cm long); flowers 6- or 7-merous

Anomanthodia* (Aidia s.l.; Aidia sect. Anomanthodia)

3*. Inflorescences not like this, terminal, flowers 4-5(6)-merous


4. Flowers of a flowering head with ovaries united by tissue fusion; fruiting head a syncarp of fused fruitlets

 Morinda p.p.

4*. Flowers and fruits of a flowering head free (but ovaries and fruits sometimes very closely spaced: Schradera!)


5. Inflorescence panicle-like, many-flowered, with numerous umbel-like partial inflorescences; fruits drupaceous, with 4 or, by abortion, only 3-1 pyrenes; leaves opposite or in whorls of 3




5*. Inflorescences not with umbel-like partial inflorescences (but entire inflorescence sometimes umbel-like, then fruits many-seeded and berry-like: Schradera!); leaves opposite


6. Corolla lobes contorted in bud and open flowers; style with very long, narrowly cylindrical entire stigma; fruit a many-seeded capsule; seeds winged


6*. Corolla lobes valvate in bud; style with distinct stigma lobes; fruit fleshy or, if dry, not a many-seeded capsule


7. Plants foetid when bruised; flowers always with a with dark purple or maroon centre and always with very short style and 2 very long, filiform stigma lobes; fruits dry, laterally compressed, the papery and brittle exocarp at length breaking open and falling off, exposing the 2 one-seeded dispersal units, or subglobose and with unwinged dispersal units


7*. Plants not with the above combination of characters


8. Flowers in globose heads; ovaries and fruits of a head tightly pressed together but not fused; individual fruitlets berry-like, many seeded; epiphytic shrub with climbing roots along internodes


8*. Plants not with the above combination of characters


9. Non-epiphytic root climber (climbing roots along internodes); inflorescence loose, several-to many-flowered, with small white flowers; calyx lobes (sub)equal; fruits drupaceous, with 2 pyrenes

Psychotria p.p.

9*. Stems without climbing roots; inflorescences ± compact; flowers never white; typically a few flowers with expanded, leaf-like, colored calyx lobes (show calyx leaves); fruits fleshy, leathery-skinned, many-seeded




KEY F. Key to Trees, treelets and shrubs (including some indistinctly straggling and scandent shrubs, and including subshrubs)

[See Note 2, above]


1. Shrub-like plants with aerial parts often woody at the base only


1*. Truly woody plants (trees, treelets, shrubs)


2. Shrubby herbs or shrublets, often unbranched and ± erect (essentially herbaceous plants ± woody at the base; without ± massive woody underground parts)


2*. Geoxylic suffrutices (subshrubs with woody underground parts and ± herbaceous to slightly woody aerial parts)


3. Inflorescence globose, head-like, ovaries of neighbouring flowers united or at least closely pressed together; fruiting inflorescence a fleshy syncarp or consisting of tightly packed drupelets

 Morinda p.p.

3*. Flowering and fruiting inflorescences not as above


4. Aerial parts of plants ± prostrate to ascending; flowers heterostylous or plants possibly dioecious (short-styled flowers possibly male, long-styled flowers possibly female), solitary or in few-flowered cymes terminal on long shoots or on short later branches; fruit berry-like, many-seeded, hairy

Aphaenandra* [Mussaenda s.l.]

4*. Aerial parts erect; inflorescence a terminal many-flowered, rather compact thyrse; flowers not heterostylous, with long-exserted style-stigma complex; fruit a glabrous drupe with 2 (or by arbortion 1) chartaceous pyrenes

Pavetta p.p. [Pavetta xxx]

5. Plants with thorns


5*. Plants without thorns


6. Stipules forming a long sheath around the internode above a node; flowers with half-superior ovaries; fruits secondarily superior


6*. Stipules not forming long sheaths (but sheaths occasionally present, although considerably shorter); flowers and fruits distinctly inferior


7. Flowers unisexual (plants dioecious or polygamo-dioecious*)


7* Flowers hermaphrodite


8. Fruit drupaceous, containing a plurilocular stone or many 1-seeded pyrenes


8*. Fruits not drupes with pyrenes


9. Calyx with persistent linear lobes; fruit with 4 hard, woody pyrenes fused into single stone; a limestone plant


9*. Calyx lobes indistinct (calyx copular, with small teeth at the most); fruit with many 1-seeded pyrenes; not on limestone


10. (At least some) inflorescences distinctly supra-axillary (arising some distance above a node); flower clusters (or sometimes solitary female flowers) subtended by a pair of boat-shaped bracts and borne on a long, filiform pedcunle; an obligate rheophyte


10*. Inflorescences not as above; plants never rheophytic


11. Treelets with +/- orthotropic paired (opposite) branches bearing opposite leaves; inflorescences paired at leafy nodes, mostly

Urophyllum / Maschalocorymbus

11*. Small trees or shrubs not as regularly branched; leaves opposite but on lateral branches seemingly in groups of 3 (simulating trifoliate leaves) due to a much shortened internode between a “normal” leaf pair and a leaf pair with only a solitary well developed leaf; inflorescences associated with pseudo-trifoliate leaves and opposite the solitary leaf;


12. Ovaries of adjacent flowers fully fused


12*. Ovaries of adjacent flowers not fused


13. Inflorescences head-like; all ovaries of a head fused


13*. Inflorescences not like that


14. Inflorescences erect, spike-, raceme- to ± head-like, consisting of ca. 3–6-flowered sessile or stalked capitula arranged along the inflorescence main axis; the flowers of a capitulum united by their ovaries


14*. Inflorescences consisting of several helicoid/scorpioid cymes radiating out from the centre in a star-like fashion; each arm on the upper side with 4 rows of flowers united by their ovaries


15. Flowers at leafless stem nodes or flowers at base of stem (plants cauli- or basiflorous)

Mycetia p.p. [M. basiflora]

15*. Plants neither cauli- nor basiflorous


16. Inflorescences very extensive and very  many-flowered panicle-like thyrses (hundreds of small flowers)


16*. Inflorescence never so many-flowered and extensive


17. Inflorescences truly axillary [see FOOTNOTE][2]; most commonly flowers in (usually) paired, (sub)sessile to (less commonly) pedunculate clusters of few to many in leaf axils of (typically) orthotropic branches; sometimes axillary inflorescences pedunculate and not condensed but variously shaped (raceme-like, with cincinnoid branches, etc.)


17*. Inflorescences truly terminal [see FOOTNOTE][2]; flowers arranged variously


18. Plants emitting a strong foetid odour (when tissue is crushed)


18*, Plants without foetid odour


19. Corolla with “normal” valvate aestivation; ovary 3-9-celled  (fruit drupaceous with 3-9 one-seeded pyrenes); lateral branches invariably solitary at main stem nodes and with leaves all in one plane

Lasianthus p.p.

19*. Corollas valvate-induplicate in bud; ovary 2-celled (fruit drupaceous with 2 one-seeded pyrenes); growth form and leaf arrangement not as above

Saprosma p.p.

20. Plants of mangroves or costal habitats


20*. Plants not in mangroves or costal habitats (if atypically so, then not with the characters given in couplet 21)


21. Plants confined to mangroves; leaves typically 4-7 by 2-4 cm; ovary 2-celled, each locule with 1 ascending and 1 pendulous ovule on a transverse placenta inserted on the middle of the septum; mature fruit dry, corky, longitudinally ridged to distinctly ribbed


21*. Plants of sandy and rocky sea shores; leaves 10-25 by 6-20 cm; ovary 4-9-celled, each locule with a pendulous solitary ovule; mature fruit a modified, hard drupe with fibrous mesocarp and 4–9 one-seeded pyrenes fused into a hard plurilocular stone


22. Flowers with (long) exserted knob-like “stylar head”; ovary 2(-3)-celled, each locule with a solitary ovule pendulous from an apical placenta


22*. Flowers never with a knob-like “stylar head”; ovary structure (placentation) different


23.  Leaves membranous to subcoriacous (but never distinctly leathery), sometimes clusterered on short shoots


23*. Leaves always coriaceous, never clustered on short shoots


24. Corolla lobes valvate in bud; ovary 3-9-celled (fruit drupaceous with 3-9 one-seeded pyrenes); lateral branches invariably solitary at main stem nodes and with leaves all in one plane


24*. Corolla lobes contorted in bud; ovary typically 2-celled (fruits various, if drupaceous with 2 pyrenes); growth form and leaf arrangement not as above


25. Flowers in paired, (sub)sessile clusters of few to +/- many

Lasianthus (s.str.)

25*. Flowers solitary or 2 on long peduncles arising in leaf axils

Litosanthes (Lasianthus s.l.)

26. Corolla lobes contorted to the right in bud; flowers relatively large (corolla tube 5-10 mm, lobes 10-20 mm long), in leaf axils or sometimes at a series of leafless nodes immediately below the leaves


26*. Corolla lobes contorted to the left in bud; flowers considerably smaller, never also at leafless nodes immediately below the leaves


27. Stipules triangular, without awn-like, aristate or +/- linear appendage at apex; inflorescences raceme-like and many-flowered to +/- condensed and fewer-flowered


27*. Stipules apically with such appendages; inflorescences consisting of (sub)sessile axillary flower clusters


28. Fruit typically 15-30 mm in diam.; seeds embedded in fleshy placental outgrowths


28*. Fruit to 10 mm (greatest length) at the most; seeds not embedded in fleshy placental outgrowths 


29. Anthers hairy around the base; upper part of style and stigma lobes densely white hairy


29*. Anthers, style and stigma lobes not hairy


30. Each ovary locule with 3-4 collateral ovules attached to an apical placenta


30*. Each ovary locule with 1-3(-6) ovules on an axile placenta


31. Leaves opposite but on lateral branches or at branch tips seemingly in groups of 3 (simulating trifoliate leaves) [leaf pair and solitary leaf close together due to much-contracted internode]


31*. No pseudo-trifoliate leaves present


32. Inflorescences consisting of pedunculate many-flowered cymes; fruits < 15 mm (greatest length)


32*. Inflorescences few-flowered to uniflorous; fruits much larger


33. On lateral branches leaf pairs alternating with solitary leaves, opposite the latter an inflorescence (nodes with leaf pairs alternating with nodes bearing a solitary leaf and a leaf-opposed inflorescence)


33*. Leaf and inflorescence arrangement not like this


34. Internodes of young branchlets on either side with a median longitudinal corky ridge which starts at a node, between the bases of a petiole pair


34*. Median longitudinal corky ridges absent


35. Fruits dry


35*. Fruits fleshy (berry-like or drupaceous, sometimes with leathery exocarp)


36. Ovary 3-5-celled; fruits with an apical operculum (falling off at maturity) and splitting into 5 valves; seeds 3-5, each loosely enclosed by the netlike interconnected vascular bundles of the endocarp


36*. Ovary 2-celled; fruits capsular, many-seeded


37. Corolla lobes valvate in bud; flowers often heterodistylous

 Hedyotis p.p.

37*. Corolla lobes not valvate in bud; flowers not distylous


38. Corolla lobes contorted in bud; capsules not woody, small (< 5 mm in diam.), with numerous minute unwinged seeds


38*. Corolla lobes imbricate in bud; capsule ± woody, at least 10 mm long; seeds with flattened bipolar wings


39. Corolla lobes valvate in bud


39. Corolla lobes contorted in bud


40. Flowers slightly zygomorphic (corolla tube curved) [if inflorescence distinctly head-like and  subtended by show-bracts see KEY D]


40*. Flowers actinomorphic; corolla tube straight


41. Corolla pale yellow to dark yellow throughout; fruit berry-like with a spongy, watery fruit wall and many small seeds; inflorescence axes thin; leaves sometimes (strongly) anisophyllous 

Mycetia p.p.

41*. Corolla white or tinged pinkish or pale lilac (but often yellow around the throat); fruit drupaceous, 2 one-seeded pyrenes; inflorescence axes distinctly succulent and swollen when in fruit (often not clear in herbarium material!)


42. Corolla pale yellow to dark yellow throughout; fruit berry-like with a spongy, watery fruit wall and many small seeds

Mycetia p.p.

42*. Corolla never yellow; fruits never berry-like and many-seeded


43. Corolla lobes valvate-induplicate in bud (the infolded lateral corolla lobe portions usually visible as 2 thin, ± wavy fringes)

Saprosma p.p.

43*. Corolla lobes with “normal” valvate aestivation (lobes thus not as above)


44. Inflorescence reduced to a solitary flower, terminal on much congested leafy or leafless short shoots (and thus seemingly appearing axillary) or on long shoots


44*. Inflorescences not uniflorous, clearly terminal, basically thyrsic and (several- to) many-flowered but very diverse in appearance (panicle-, corymb-, spike- or head-like)

 Psychotria p.p.

45. Flowers consistently 4-merous


45*. Flowers 5-merous, or number of corolla lobes increased to 10(11)


46. Leaves typically with bacterial nodules (dark spots on leaf blades in herbarium material), stipules triangular cuspidate; style very long, slender, long-exserted from corolla tube, the stigmatic surface a small 2-lobed area at the apex


46*. Leaves never with bacterial nodules; stipules often triangular, typically with a (±) long awn at the apex; style with 2-lobed stigma exserted (but not as conspicuously as above), stigma lobes often recurved


47. Ovary 2-celled, each locule with a solitary ovule on a small placenta attached to the middle (or above the middle) of the septum; style short, with 2 small stigma lobes, included; fruit an often 2-lobed drupe with 2 pyrenes; inflorescence terminal on stems (long shoots) or sometimes terminal on axillary short shoots, 5- to 1-flowered


47*. Not with the above combination of characters


48. Young stems and branches often distinctly 4-angled; fruits berry-like (exocarp skin-like but never thick and leathery), with 1 to several seeds in each locule


48*. Young stems and branches not distinctly 4-angled; fruits with a with thick, leathery skin (rarely at length +/- irregularly splitting open), with many to very many seeds, typically embedded in a fleshy mass (= proliferating placental tissue


49. Ovary unilocular, placentation parietal, placentas 2–9 


49*. Ovary 2-locular, placentas attached to septum , always 2


50. Young parts, shoot tips and buds often coated with a resinous exudate (or at least shoot tip with a droplet of +/- colorless, yellowish or orange exudate); corolla lobes (4)5-10(11); placentas 2–9


50*. Plants without conspicuous resinous exudate; corolla lobes mostly 5; placentas 2


51. Stipules connate into a sheathing tube but bilobed above and persistent (without an abscission zone above the petioles)


51*. Stipules not like that


52. Inflorescences reduced to solitary flowers


52*. Inflorescences more-flowered


53. Corolla tube 6–8 cm long


53*. Corolla tube shorter


54. Leaves anisophyllous; flowers large, anthers and stigmas included; fruits large (to 4 cm long)


54*. Leaves isophyllous; flowers small, anthers and stigmas exserted; fruits much smaller





[1] C. Puff

[2] NOTE: careful examination is necessary: inflorescences borne terminally on much-contracted lateral short shoots may give the false impression of being axillary (“pseudoaxillary inflorescences”); inflorescence borne opposite a single leaf (“leaf-opposed inflorescences”), too, are not axillary!