00. mitragyna[1]

Korth., Observ. Naucl. Indic.: 19 (1839), nom. cons.; Ridsdale, Blumea 24: 56. 1978; Puff et al., Rubiaceae of Thailand: 46 & pl. 3.1.1. 2005.— Stephegyne Korth., Verh. Nat. Gesch. Ned. Bot.: 160 & t. 35. 1842.— Paradina Pierre ex Pitard in Fl. Gén. I.-C. 3(1): 39. 1922.

Small to fairly large trees. Leaves opposite, petiolate, blades chartaceous to subcori­aceous; stipules interpetiolar, entire, with a central keel, often large and ovate to lanceolate, caducous; young foliage (at least midrib), and sometimes also stipules, occasionally reddish to reddish-purplish []. Inflorescences consisting of globose, many-flowered flowering heads terminal on lateral branches and on their (sometimes repeatedly branched) side shoots, often arranged like simple or compound dichasia, like thyrses, or like pseudo-umbels; young heads subtended by a pair of (small) leaves with enlarged, sometimes somewhat colored deciduous stipules, or only the involucre-like enlarged stipules; flowering heads with linear to spathulate interfloral bracteoles []. Flowers 5-merous, hermaphrodite, (sub)sessile. Calyx with a basal tubular part and variously shaped lobes. Corolla infundibular to narrowly hypocra­teriform, tube hairy around the throat, lobes valvate in bud, ascending in open flowers. Stamens inserted at or just below the throat, filaments short, usually at least the anthers exserted. Ovary 2-celled, each locule with numerous ovules on an elongated placenta attached to upper part of septum; ovaries of adjoining flowers of a head not fused with each other; style with mitriform to elongate, clavate stigma exserted. Fruitlets of a fruiting head free from one another, crowned by the persistent calyx, ellipsoid to ovoid, capsular, dehiscing septicidally and then loculicidally from the apex downwards. Seeds small, numerous, slightly winged at both ends, the lower wing ± bifid.

A genus of 6 species centered in continental SE. Asia and the Male­sian region (if delimited narrowly and the African Hallea Leroy is recognized as generically distinct); 4 species in Thailand.— Classification: subfamily Cinchonoideae, tribe Naucleeae.

Key to the species

As vegetative characters are variable and often overlap between species, it is necessary to use bracteoles and calyces to correctly identify species (hand lens and precise measurements are needed!)

1. Calyx lobes linear to linear-spathulate, 2-2.5 mm long

      2. M. hirsuta

1*.  Calyx lobes not linear, obtuse to rounded or triangular, to 1.5 mm long

  2

2. Interfloral bracteoles 4-6 mm long, in young flowering heads conspicuous (i.e., interfloral bracteoles longer than ovary plus calyx); leaves with (8)11-17 pairs of lateral veins

4. M. speciosa

2*. Interfloral bracteoles to 3 mm long, in young flowering heads concealed (i.e., ovary plus calyx longer than interfloral bracteoles) or visible (i.e. interfloral bracteoles about as long as the ovary); leaves with 5-10 pairs of lateral veins

 3

3. Entire calyx c. 1.5 mm high, about the same length as the ovary; interfloral bracteoles about as long as the ovary (hence calyx lobes visible in the young heads); leaves typically 6-14 by 3-9 cm, with quite “steep” lateral veins (angle between midrib and veins c. 10-30°)

1. M. diversifolia

3*. Entire calyx < 1 mm high, less than half the length of the ovary; interfloral bracteoles longer than or about as long as ovary and calyx (hence interfloral bracteoles clearly visible in young flowering heads); leaves typically larger (14-25 by 10-20 cm), with relatively “flat” lateral veins (angle between midrib and veins c. 30-55°)

3. M. rotundifolia

1. Mitragyna diversifolia (Wall. ex G.Don) Havil., J. Linn. Soc., Bot. 33: 71. 1897;  Ridsdale, Blumea 24: 65. 1978.— Nauclea diversifolia Wall. ex G.Don, Gen. Hist. 3: 467. 1834.— Stephegyne diversifolia (Wall. ex G.Don) Hook.f., Fl. Br. Ind. 3: 26. 1880, pro parte.— Nauclea parvifolia Roxb. var. diversifolia (Wall. ex G.Don) Kurz, For. Fl. Burm. 2: 67. 1877.—  Mitragyna javanica Koord. & Val., Bijdr. 8: 38. 1902; Koord., Altas Baumarten Javas, 3(11): fig. 513. 1915. — Stephegyne parvifolia sensu Pitard in Fl. Gén. I.-C. 3(1): 42. 1922, non Roxb.— Mitragyna diversifolia (Wall. ex G.Don) Havil. var. microphylla sensu Craib, Kew Bull. Misc Inf. 1911: 386. 1911, pro parte, Craib, Aberdeen Univ. Stud. 57: 99. 1912, pro parte, non (Kurz) Craib.*— Mitragyna javanica Koord. & Val. var. microphylla sensu Craib in Fl. Siam. En. 2(1): 12. 1932, pro parte, non (Kurz) Craib.*

* “Var. microphylla” has been wrongly applied to small-leaved plants of M. diversifolia from Thailand. The variety is associated with M. parvifolia (Roxb.) Korth. [var. microphylla (Kurz) Ridsdale; syn. Nauclea parvifolia Roxb. var. microphylla Kurz], a taxon not recorded from Thailand.

Deciduous small tree  to c. 8 m, rarely taller; bark grey to dark grey-brown; terminal vegetative bud obovate to oblong in outline, flattened. Leaves chartaceous to subcoriaceous, oblong, obovate or orbicular, (4)6-14(16) by (2.5)3-9(12) cm, base rounded to obtuse, rarely ± cuneate,  apex rounded or obtuse, glabrous above, below pubescent along the veins only; 5-10 pairs of quite “steep” lateral veins (angle between midrib and veins c. 10-30°), hairy domatia present in vein axils; petioles 1-2.5 cm long, pubescent; stipules obovate to oblong, 10-15 by 5-10 mm, often slightly keeled, outside pubescent. Inflorescences terminal on often repeatedly branched side shoots of the main lateral branches, consisting of (3)5-9(15) flowering heads in thyrse- to pseudo-umbel-like arrangement. Flowering heads c. 6-10 mm in diam. across calyces and 15-20 mm across corollas; interfloral bracteoles linear-spathulate, 2-3 mm long, usually glabrous, exceptionally ciliate, reaching about the same length as the ovaries [hence calyx lobes clearly visible in the young heads]. Calyx glabrous, tubular below and with obtuse to rounded or broadly triangular lobes above, entire calyx c. 1.5 mm high. Corolla creamy white to (pale) yellow, often turning darker with age; tube hypocrateriform to narrowly infundibular, 3-4 mm long, outside glabrous, inside densely hairy, hairs protruding from the throat; lobes narrowly elliptic, 2.5-3.5 mm long, inside hairy at base, outside glabrous. Stamens with filaments to 1 mm long, anthers 1.5-2 mm long, exserted from the throat, spreading. Ovary c. 1.5 mm high, glabrous; style plus stigma exserted for 6-7 mm, stigma 1.5-2 mm long. Individual fruitlets c. 5 mm long, glabrous, crowned by the persistent calyx. Fruiting head 13-18 mm in diam.

T h a i l a n d.— NORTHERN: Chiang Mai, Chiang Rai Lamphun, Phitsanulok, Kamphaeng Phet, Nakhon Sawan; NORTH-EASTERN: Loei; EASTERN: Chaiyaphum; SOUTH-WESTERN: Ratchaburi; central: Chai Nat, Saraburi, Pathum Thani, Krung Thep Maha Nakhon (Bangkok); SOUTH-EASTERN: Prachin Buri; PENINSULAR: Surat Thani, Nakhon Si Thammarat, Satun.

D i s t r i b u t i o n.— Myanmar, Indochina, China (Yunnan); Peninsular Malaysia, Java, Philippines.

E c o l o g y.— Dry dipterocarp forest, dry deciduous forest; often in disturbed sites such as old rice fields; frequently left as shade tree at the edge of rice fields. Altitude: 0–400 m. Flowers July - August, fruits November - February.

V e r n a c u l a r.— ???.

2. Mitragyna hirsuta Havil., J. Linn. Soc., Bot. 33: 72. 1897; Craib in Fl. Siam. En. 2(1): 12. 1932; Ridsdale, Blumea 24: 59 & fig. 6. 1978.— Paradina hirsuta Pitard in Fl. Gén. I.-C. 3(1): 39. 1922. Fig. MITh.

Deciduous small tree  to c. 10 m, rarely taller; bark grey, scaly; terminal vegetative bud ovate to elliptic in outline, somewhat flattened. Leaves chartaceous, broadly ovate or orbicular to elliptic, (8)10-18 by 4-12(15) cm, base rounded to cordate, rarely ± cuneate,  apex rounded to acute, glabrous above, sparsely to densely pubescent below; 6-12 pairs of relatively “steep” lateral veins (angle between midrib and veins c. 15-45°), sparsely to densely hairy domatia present in vein axils; petioles (1)1.5-3 cm long; stipules ovate to elliptic, 10-20 by 8-15 mm, slightly keeled, outside pubescent, particularly on the keel and veins. Inflorescences terminal on often repeatedly branched side shoots of the main lateral branches, consisting of (5)7-15(30) flowering heads in thyrse- to pseudo-umbel-like arrangement. Flowering heads c. 10 mm in diam. across calyces and 20-30 mm across corollas; interfloral bracteoles linear to linear-spathulate, 2.5-3.5 mm long, glabrous to slightly pubescent, reaching about the same level as the calyx lobes. Calyx tube almost completely reduced, lobes linear to linear-spathulate, 2-2.5 mm long, glabrous to sparsely hairy. Corolla (pale) yellow, often turning orange-yellow with age; tube hypocrateriform to narrowly infundibular, 5-6 mm long, outside glabrous, inside densely hairy, hairs protruding from the throat; lobes elliptic, 2-2.5 mm long, inside hairy at base, outside glabrous. Stamens subsessile, anthers 1.5-2 mm long, exserted from the throat, spreading. Ovary c. 1-2 mm high, glabrous; style plus stigma exserted for 5-6 mm, stigma 1-2 mm long. Individual fruitlets 5-8 mm long, glabrous, crowned by the persistent calyx lobes. Fruiting head 15-20 mm in diam.

T h a i l a n d.— NORTHERN: Chiang Mai, Phrae, Nakhon Sawan; NORTH-EASTERN: Phetchabun, Loei, Sakon Nakhon, Mukdahan, Khon Kaen; EASTERN: Nakhon Ratchasima, Ubon Ratchathani; SOUTH-WESTERN: Ratchaburi, Phetchaburi.

D i s t r i b u t i o n.— Laos, Cambodia, Vietnam (type); possibly extending into Myanmar.

E c o l o g y.— In various deciduous forest types; often in disturbed sites such as roadsides. Altitude: <50–680 m.

V e r n a c u l a r.— ???.

3. Mitragyna rotundifolia (Roxb.) O. Kuntze, Rev. Gen. Pl. 1: 289. 1891; Craib in Fl. Siam. En. 2(1): 14. 1932; Ridsdale in Blumea 24: 65 & fig. 8 (1978).— Nauclea rotundifolia Roxb. [Hort. Beng. 66. 1814, nom. nud.] Fl. Ind. ed. 1, 2: 14. 1824, Fl. Ind. ed. 2, 1: 516. 1832; Kurz, For. Fl. Burm. 2: 67. 1877.— Nauclea brunonis Wall. ex G.Don, Gen. Hist. 3: 467. 1834.— Mitragyna brunonis (Wall. ex G.Don) Craib in Fl. Siam. En. 2(1): 11. 1932.— Stephegyne diversifolia sensu Pitard in Fl. Gén. I.-C. 3(1): 43. 1922, non (Wall. ex G.Don) Hook.f. Fig. MITr.

Deciduous tree to c. 30 m tall (but frequently smaller); bark light greyish-brown, longitudinally fissured; terminal vegetative bud elliptic to obovate in outline, strongly flattened. Leaves chartaceous, orbicular to broadly elliptic or (broadly-)ovate, (10)14-25 by (7)10-20 cm, base rounded to cordate, apex rounded to acute, glabrous above, pubescent to densely pubescent below; 6-10 pairs of relatively “flat” lateral veins (angle between midrib and veins c. 30-55°); petioles 2-6 cm long; stipules elliptic(-oblong) to obovate 10-40 by 5-15 mm, keeled, outside pubescent, particularly on the keel and veins. Inflorescences terminal on often repeatedly branched side shoots of the main lateral branches, consisting of (3)7-15(20) flowering heads in thyrse- to pseudo-umbel-like arrangement. Flowering heads to 10 mm in diam. across calyces and 15-20 mm across corollas; interfloral bracteoles linear-spathulate, 2.5-3 mm long, ciliate on the margins or less commonly glabrous, longer than or about as long as ovary and calyx (hence clearly visible in young flowering heads). Calyx tube (sub)obsolete, lobes minute, obtuse, to 0.5 mm long, glabrous. Corolla (pale) yellow, often turning orange-yellow with age; tube hypocrateriform to narrowly infundibular, 2-3.5 mm long, outside glabrous, inside densely hairy, hairs protruding from the throat; lobes narrowly elliptic, 2-2.5 mm long, inside hairy at base, outside glabrous. Stamens subsessile, anthers 1-2 mm long, exserted from the throat, spreading. Ovary c. 2-2.5 mm high, glabrous; style plus stigma exserted for 4-6 mm, stigma 1.5-2 mm long. Individual fruitlets 3-5 mm long, glabrous, crowned by the minute persistent calyx lobes. Fruiting head 10-16 mm in diam. -fig. A-G

T h a i l a n d.— NORTHERN: Mae Hong Son, Chiang Mai, Nan, Phrae, Kamphaeng Phet; NORTH-EASTERN: Nong Bua Lum Phu, Maha Sarakham; SOUTH-WESTERN: Ratchaburi, Kanchanaburi.

D i s t r i b u t i o n.— E. India (type), Bangladesh, Myanmar, Laos.

E c o l o g y.— In various deciduous forest types; often in disturbed places such as along roads or in secondary scrub and thicket; sometimes over limestone. Altitude: 10–500 m.

V e r n a c u l a r.— ???.

4. Mitragyna speciosa (Korth.) Havil., J. Linn. Soc. Bot. 33: 69. 1897; Craib in Fl. Siam. En. 2(1): 14. 1932; Ridsdale in Blumea 24: 65. 1978.— Stephegyne speciosa Kort., Verh. Nat. Gesch. Bot.: 160. 1840.— Nauclea speciosa (Kort.) Miq., Fl. Ind. Bat. 2: 140. 1857, nom. illeg., non Wall. ex G.Don.

Briefly deciduous (sometimes evergreen?) tree to 25 m tall; bark grey to greyish-brown, smooth; terminal vegetative bud lanceolate in outline, flattened. Leaves chartaceous to subcoriaceous, elliptic to slightly ovate or obovate, 5-17 by 3-12 cm, base rounded to cordate, apex acute, glabrous above and below or slightly hairy on lower surface only; (8)11-17 pairs of relatively “flat” lateral veins (angle between midrib and veins c. 20-60°), pale-hairy domatia present in vein axils; petioles (1)2.5-5 cm long; stipules lanceolate, to 40 by 10 mm, keeled. Inflorescence a terminal, solitary, pedunculate flowering head, the latter with pale-hairy, spathulate interfloral bracteoles 4-6 mm long, longer than ovary plus calyx (hence calyces concealed by interfloral bracteoles in your flowering heads). Flowering heads 9-13 mm across interfloral brac­teoles, 15-25 mm across corollas. Calyx sometimes pinkish, tube to 2 mm long, lobes hardly developed. Corolla creamy white to yellowish-white, turning darker with age; tube 3.5-5 mm long, outside glabrous, inside densely hairy, hairs protruding from the throat; lobes 2.5-3 mm. Stamens subsessile, anthers 1-1.5 mm long, exserted from the throat, spreading. Ovary c. 1.5-2 mm high, glabrous; style plus stigma exserted for 3-5 mm, stigma 1-2 mm long. Individual fruitlets 7-9 mm long, glabrous, crowned by the persistent calyx. Fruiting head 20-30 mm in diam.

T h a i l a n d.— central: Krung Thep Maha Nakhon (Bangkok) [cultivated]; SOUTH-WESTERN: Ratchaburi; PENINSULAR: Phangnga.

D i s t r i b u t i o n.— Peninsular Malaysia, Sumatra, Borneo, Philippines, New Guinea; S. Vietnam (cultivated).

E c o l o g y.— Mostly in lowland evergreen forest, often in moist to wet places along streams; occasionally also in swamp forest. Altitude: <50–200 m.

V e r n a c u l a r.— Kratom ???.

U s e s.—  Various traditional uses: to treat diarrhea; as a stimulant; as an opium substitute. In recent years Kratom has gained popularity as recreational drug, due to its narcotic-like effects, producing feelings of euphoria similar to heroin. Typically, fresh leaves are chewed, but dried leaves are sometimes smoked or made into powder and drunk as tea [see http://www.mitragyna.com/index.php]

N o t e.— Although frequently cultivated in the Peninsula, the species also occurs naturally.


Fig. MITh. Mitragyna hirsuta Havil., a. shoots with fruiting heads and with terminal vegetative bud; b. shoots with young flowering heads; c. flower; d. fruit (not yet dehisced) with persistent calyx and some interfloral bracteoles. [from Ridsdale 1978]

Fig. MITr. Mitragyna rotundifolia (Roxb.) O. Kuntze, a. shoot with young flowering heads; b. shoots with fruiting heads ; c. node with base of petioles and (slightly supraaxillarly) branches; d. flower. [from Ridsdale 1978]



[1] C. Puff