Flora of Thailand



70. Pedilanthus


H.-J. Esser


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Genus description

Species description

Key to the subspecies

subsp. tithymaloides

subsp. smallii




Necker ex Poit., Ann. Mus. Nat. Hist. Nat. 19: 388. 1812; Boiss. in DC., Prodr. 15, 2: 4. 1862; Millsp., Field Mus. Publ. Bot. 2: 353. 1913; Pax & K.Hoffm. in Engl. & Harms, Nat. Pflanzenfam. ed. 2, 19c: 223. 1931; Dressler, Contrib. Gray Herb. 182: 97. 1957; G.L.Webster, J. Arnold Arbor. 48: 427. 1967; Ann. Missouri Bot. Gard. 81: 130. 1994; Radcl.-Sm., Gen. Euphorbiacearum: 418. 2001; Esser in in Welzen & Chayam., Fl. Thailand 8, 2: 470. 2007; G.L.Webster in Kubitzki, Fam. Gen. Vasc. Pl. 11: 207 (sub Euphorbia). 2014Tithymalus Mill., Gard. Dict. Abr. Ed. 4: 3. 1754, nom. rejic Tithymaloides Ortega, Tab. Bot.: 9. 1883, nom. rejic.— Ventenatia Tratt., Gen. Pl. 86: 1802 (non Cav., 1798).— Crepidaria Haw., Syn. Pl. Succ.: 136. 1812.— Diadenaria Klotzsch & Garcke, Monatsber. Königl. Preuss. Akad. Wiss. Berlin: 254. 1859.— Hexadenia Klotzsch & Garcke, Monatsber. Königl. Preuss. Akad. Wiss. Berlin: 253. 1859.


Shrubs or trees, monoecious, succulent or not, not spiny; unbranched or with alternate branching; latex white. Indumentum absent or consisting of multicellular, unbranched hairs. Stipules small, blunt. Leaves alternate, distichous; petiole short to absent; blade simple, symmetric, eglandular. Inflorescences as cyathia, pseudanthial, distinctly zygomorphic, involucral bracts 5, partly glandular, partly connate, forming a zygomorphic tube, with 2, 4 or 6 glands, their appendages partly connate and forming a spur; cyathia in terminal or axillary, cymose inflorescences, their bracts large or small. Individual flowers with much reduced to absent sepals, without petals or disc; bracteoles present and filamentous or absent. Staminate flowers lateral, numerous, in 5 groups, reduced to a single stamen; anther 2-locular, basifixed. Pistillate flower terminal, pedicellate, consisting only of the reduced to absent calyx and the ovary; ovary 3-locular, smooth, with 1 ovule per carpel; style present, stigmas apically bifid. Fruits 3-locular, smooth, dry and dehiscent. Seeds 3 per fruit, ovate-elliptic, glabrous, with smooth or sculptured surface, dry, ecarunculate.

    Fourteen species, 13 of which restricted to Mexico, Central America and the Antilles, only one with a wide distribution from the USA (Florida) to the West Indies and South America and cultivated in all tropical regions including Thailand. Classification: Subfam. Euphorbioideae, tribe Euhorbieae.


Pedilanthus tithymaloides (L.) Poit., Ann. Mus. Nat. Hist. Nat. 19: 390, pl. 19. 1812; Kurz, Forest Fl. Burma 2: 418. 1877; Dressler, Contrib. Gray Herb. 182: 137. 1957; Fl. Bhutan 1: 763, pl. 47 c, d. 1987; Wijnands, Bot. Commelijns: 104. 1983; J.S. Ma, Fl. Reipubl. Pop. Sin. 44(3): 128. 1997; Esser in  in Welzen & Chayam., Fl. Thailand 8, 2: 4471, Fig. 53.— Euphorbia tithymaloides L., Sp. Pl.: 453. 1753.


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Shrubs to c. 2 m tall, with succulent stem, deciduous and usually flowering when leafless. Indumentum present on young parts, later glabrous. Stipules c. 0.5 mm long, caducous. Leaves slightly succulent; petiole 2-5 mm long; blade ovate to elliptic, base attenuate, margin entire, apex acute to obtuse, slightly brighter below venation hardly visible, midvein strongly keeled below, side veins c. 9 pairs, not triplinerved. Cyathia partly red (in particular spur), partly green, spur short (less than 3 mm long), bracts less than 15 mm long, glands 4. Fruits 5-6 mm in diam., sulcate. Seeds subglobose, 3-4.5 by 2.5-3 mm, grey-brown (not known from Thailand).

    T h a i l a n d.— Common in cultivation, but rarely collected.

    D i s t r i b u t i o n.— The most widespread species of the genus, from the USA (Florida) to northern South-America and most of the Antilles. Eight subspecies distinguished, most of them local endemics on the Antilles.

    E c o l o g y.— In the Americas, growing in a wide range of habitats, in coastal scrub, arid thorn forest, dry deciduous forest, or in exposed, rocky sites of more humid environments, and more frequent on limestone.

    V e r n a c u l a rSayaek (แสยก) (Central).

    U s e s.— Garden ornamental, often utilised as low hedge.

    N o t e.— The distinction between the subspecies seems to be less clearcut in Thailand than in their American origin. Dressler, in the latest revision of Pedilanthus, attributed the cultivated plants of tropical Asia to subsp. smallii, but based on leaf sizes most of the Thai plants studied must be attributed to subsp. tithymaloides despite their notably zig-zag stems.


Key to the subspecies



Stems markedly and conspicuously zig-zag; young leaves and stems glabrous to sparsely pubescent; blades 2.5-7 by 1.3-3.2 cm; cyathial bracts 5-7 mm long.

1a. subsp. smallii


Stems straight to moderately zig-zag; young leaves and stems glabrous to densely pubescent; blades 1-16 by 0.8-10 cm; cyathial bracts 4-14 mm long.

1b. subsp. tithymaloides


subsp. tithymaloides: Esser in Welzen & Chayam., Fl. Thailand 8, 2: 473. 2007


    D i s t r i b u t i o n.— Mexico to Central- and South-America up to Suriname, but widely cultivated, also as greenhouse plant. The most widespread and variable of all subspecies.

    V e r n a c u l a r.— Ka yaek, maha prasan, sayaek, sayaek sam si, yang (Central), khia kai hai, nang kwak, wan sali (Northern), ta-si ka-mo (Karen-Mae Hong Son), Slipper flower.


subsp. smallii (Millsp.) Dressler, Contrib. Gray Herb. 182: 152. 1957; Esser in Welzen & Chayam., Fl. Thailand 8, 2: 473. 2007Pedilanthus smallii Millsp., Field Mus. Pub. Bot. 2: 358. 1913.— Tithymalus smallii (Millsp.) Small, Man. S.E. Flora: 804. 1933.


    D i s t r i b u t i o n.— USA (Florida) and Cuba, but widely cultivated throughout the tropics.

    V e r n a c u l a r.— Sayaek bai yik (แสยกใบหยิก) (Bangkok).