Malesian Euphorbiaceae Descriptions

55. HEVEA (Euphorbiaceae)

Hoang Van Sam & P.C. van Welzen

Hoang Van Sam & P.C. van Welzen. 2004. Revision of Annesijoa, Elateriospermum and

the introduced species of Hevea in Malesia (Euphorbiaceae). Blumea 49: 425–440.

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Genus description

Key to the Malesian species

Species descriptions

Hevea Aubl.

    Hevea Aubl., Hist. Pl. Guiane 2 (1775) 871, t. 335; Müll.Arg. in A.DC., Prodr. 15, 2 (1866) 716; Pax in Engl., Pflanzenr. IV.147.i (1910) 117; Ducke, Arq. Inst. Biol. Veg. 2 (1935) 217; Corner, Wayside Trees Mal. 1 (1940) 256; R.E.Schult., Bot. Rev. 36 (1970) 197; Regnum Veg. 71 (1970) 229; Bot. Mus. Leafl. 25 (1977) 243; Econ. Bot. 41 (1987) 125; G.L.Webster, Ann. Missouri Bot. Gard. 81 (1994) 99; Radcl.-Sm., Gen. Euphorbiacearum (2001) 271; Hoang Van Sam & Welzen, Blumea 49 (2004) 433; Welzen in Welzen & Chayam., Fl. Thailand 8, 2 (2007) 331; G.L.Webster in Kubitzki, Fam. Gen. Vasc. Pl. 11 (2014) 164, Fig. 38. — Type: Hevea guianensis Aubl.

    Siphonia Rich. in Schreb., Gen. Pl., ed. 8, 2 (1791) 656, nom. superfl. — Lectotype (designated by Webster, 1994): Siphonia elastica Pers. [= Hevea guianensis Aubl.].

    Caoutchoua J.F.Gmel., Syst. Nat., ed. 13, 2 (1791) 677, nom. superfl. — Type: Caoutchoua elastica J.F.Gmel. [= Hevea guianensis Aubl.].

    Micrandra R.Br. in Benn. & R. Br. (non Benth.), Pl. Jav. Rar.  (1844) 237, nom. rejic. — Type: Micrandra ternata R.Br. [= Hevea guianensis Aubl.].

    Siphonanthus Schreb. ex Baill., Étude Euphorb. (1858) 324. — Type: Siphonanthus elastica Schreb. ex Baill. [= Hevea guianensis Aubl.].

Monoecious trees. Latex white. Indumentum of simple hairs, glabrous except for inflorescence and sometimes the lower leaf surface. Stipules very early caducous. Leaves alternate, trifoliolate, long petiolate; leaflets symmetric, papery, basally attached, with 2 or 3 glands at the base, margin entire to wavy; venation pinnate, nerves looped and closed near margin, veins scalariform, veinlets reticulate. Inflorescences axillary to pseudoterminal panicles, single per axil, often in groups; bracts small, triangular; staminate flowers in cymules, pistillate flowers single at end of branches. Flowers actinomorphic; calyx 5-lobed, valvate, lobes ovate, apically pointed and often bent; petals absent, disc glands absent or 5, free or united, opposite sepalous. Staminate flowers: stamens 4–10, filaments united, in 1 or 2 layers above each other, anthers free, 2-locular, sessile; pistillode present. Pistillate flowers: calyx basally thickened, ovary 3- or 4-locular, apically beaked; ovules 1 per locule; stigmas sessile with horizontal short lobes. Fruits large capsules, trilobed, obtusely or acutely trigonous, septicidally dehiscent into three bivalved cocci (partly dehisced loculicidally), endocarp woody, column persistent. Seeds ellipsoid, ecarunculate, testa crustaceous, smooth, marbled; endosperm scanty or absent; cotyledons thick.

    Distribution — Ten species in Amazonian South America, one of great economic importance and found cultivated throughout the tropics. Two other species occasionally present in Malesian botanical gardens.

Key to the Malesian species

1. Hevea brasiliensis (Willd. ex A. Juss.) Müll.Arg.

    Hevea brasiliensis (Willd. ex A. Juss.) Müll.Arg., Linnaea 34 (1865) 204; in A.DC., Prodr. 15, 2 (1866) 718; Pax in Engl., Pflanzenr. IV.147.i (1910) 121; Ducke, Arq. Inst. Biol. Veg. 2 ( 1935) 226; Corner, Wayside Trees Mal. 1 (1940) 256; R.E.Schult., Bot. Mus. Leafl. 14 (1950) 79; Bot. Mus. Leafl. 16 (1953) 26; Bot. Rev. 36 (1970) 197; Regnum Veg. 71 (1970) 239; Bot. Mus. Leafl. 25 (1977) 243; Econ. Bot. 41 (1987) 125; Radcl.-Sm., Fl. Trop. E. Africa. Euphorbiaceae (1987) 183, f. 36; Ghani & Wessel in E.Boer & Ella, PROSEA 18 (Plants producing exudates) (2001) 73; Hoang Van Sam & Welzen, Blumea 49 (2004) 434, fig. 3; Welzen in Welzen & Chayam., Fl. Thailand 8, 2 (2007) 332, Fig. 6, Plate XVII: 4. — Siphonia brasiliensis Willd. ex A. Juss., Euphorb. Gen. (1824) pl. 12: 38 (see note). — Lectotype (Schultes, 1950): F.G. Sieber via Hoffmansegg in Herb. Willdenow sheet 17936 (holo B-WILLD; iso in G, P n.v.; IDC microfiche 7440-29, negative 1028/2), Brazil, Pará Prov., Rio Amazonas.

For other synonyms see the various publications of R.E. Schultes (esp. 1950, 1970, 1970, 1987).

Tree, up to 30 m high. Stipules not seen. Leaves: petiole 3–23.2 cm long; petiolules 5–10 mm long; leaflets elliptic or obovate, 5–23.5 by 2.2–8.8 cm, length/width ratio 2.3–2.7, reclinate, base attenuate, apex acuminate to cuspidate, both surfaces glabrous, venation distinct on both sides, nerves 14–27 till apex, flat above, raised underneath. Inflorescences up to 31 cm long, glabrous to hairy, branches up to 6.2 cm long, peduncle 1–4.6 cm long; bracts 5–8 by 2–4 mm. Staminate flowers 4.5–5 mm diam., yellowish, sweet scented; pedicel 0.6–3.2 mm long; calyx 4.5–6.2 mm long, lobes 2–4.5 by 0.5–1.5 mm; androphore 2.2–2.8 mm long, stamens 10, united in two layers, anthers 0.5–0.8 by 0.2–0.3 mm; disc glands absent; pistillode 0.8–1 mm long. Pistillate flowers 5–5.6 mm diam.; calyx 5–7.4 mm high, lobes 3–4.5 by 1–1.8 mm; disc glands absent; ovary 2–2.4 by 1.8–2.1 mm, hairs on ovary; stigmas c. 0.2 mm long. Fruits 4–5 by 3.2–4.8 cm, wall 3–4 mm thick, unripe green, brown when ripe; pedicel 0.6–2.5 cm long; column 25–32 mm long. Seeds 2.3–2.6 by 1.9–2.1 by 1.4–1.6 cm.

    Distribution — Only known from cultivation, originally only from Amazonian South America, presently cultivated worldwide in tropical regions.

    Habitat & Ecology — Reported wild and common in evergreen forest, probably escaped from abandoned plantations; once reported from limestone. Altitude: sea level up to 200 m. Flowering and fruiting throughout the year.

    Uses — Of high economic value. The bark is tapped for its latex by making shallow, V-shaped cuts over 1/3 of the circumference, working from c. 2 m high toward the root, moving to the next third once a row is finished. The latex comprises elastic strings of polymers of cis-polyisoprene, which, when still unvulcanised, are easily detached from each other and they are therefore used in chewing gum [NB: Hevea is one of the few Euphorbiaceae with a non-poisonous latex]. Vulcanised (mixed with sulphur and baked) the strings become solidly attached to each other and have many applications as rubber. Natural rubber is more elastic and durable than artificial rubbers. Its main use is undoubtedly in tires (next to condoms due to the HIV virus). The tires are presently more and more re-used as furniture, shoes, and waste baskets in SE Asia and in a new kind of tarmac in Europe.

    When the latex production of the fast growing trees decreases they are cut and the wood, though not durable and strong, is more and more used in Thailand for the production of beautiful, light coloured furniture and wooden toys for children.

    Vernacular names — General names: Para rubber, rubber (English). Viet Nam: Cao su. Malay Peninsula: Gehta para, ka-toh. Sumatra: Para (Jami). Java: Karet kipia, Cautchuc. Borneo (Sabah): Fatok para ( Bidayuh).

    Note — The interpretation of Hevea brasiliensis is difficult, because it is only known from cultivation and, consequently, many synonyms, varieties, cultivars, etc. have been described in the course of time. This is not the only difficulty, also the correct interpretation of the concept of the species and the first publication of the name are troublesome. De Jussieu (1824) published the name Siphonia brasiliensis first, but this is apparently a nomen nudum. Luckily the ICBN allows detailed drawings to be valid descriptions and De Jussieu’s plate is very detailed. This is fortunate because one year later Kunth (1825) also used the name Siphonia brasiliensis for two distinct plants, one from Venezuela (Orinoco) and the other from Brazil (lower Amazon). The latter is the cultivated species. De Jussieu used a specimen from the Willdenow herbarium. There are three sheets named Siphonia brasiliensis, but only one is identified as Hevea brasiliensis by Schultes, the others bear the identification H. pauciflora. This means that only one sheet should be taken as lectotype.

2. Hevea guianensis Aubl.

    Hevea guianensis Aubl., Hist. Pl. Guiane 2 (1775) 871, t. 335; Müll.Arg., Linnaea 34 (1865) 204; in A.DC., Prodr. 15, 2 (1866) 719; Pax in Engl., Pflanzenr. IV.147.i (1910) 127, f. 44; Ducke, Arq. Inst. Biol. Veg. 2 ( 1935) 223; R.E.Schult., Bot. Rev. 36 (1970) 222; Regnum Veg. 71 (1970) 235; Bot. Mus. Leafl. 25 (1977) 243; Hoang Van Sam & Welzen, Blumea 49 (2004) 437. — Caoutchoua guianensis (Aubl.) O.F.Cook, J. Wash. Acad. Sci. 31 (1941) 58 — Type: Aublet s.n. (BM), Guianas, Cayenne, 1775.

This species is rather variable and widespread, many synonyms exist (see Pax, 1910; Schultes, 1970 & 1970).

Tree, up to 40 m; foliage dense and very dark. Stipules not seen. Leaves: petiole 4.5–9 (–28) cm long; petiolules 6–10 mm long; leaflets elliptic to obovate, 5.4–15.2(–33.8) by 2.7–5.3(–10.2) cm, length/width ratio 2–3.3, erect, base obtuse to cuneate, apex rounded to acuminate at apex, upper surface glabrous, lower surface hairy, venation flat above, raised underneath, nerves 9–25 till apex. Inflorescences up to 20.2 cm long, pubescent, branches up to 7.3 cm long; bracts c. 1.2 by 0.3 mm. Staminate flowers 4–4.5 mm diam.; pedicel 2–8 mm long; calyx 4–4.7 mm high, lobes 1.5–2.2 by 0.8–1.5 mm, stamens (4 or) 5 (or 6) forming a single regular verticil, but some specimens having one anther inserted a little below the others, anthers 0.5–0.7 by 0.2–0.3 mm; disc glands absent; pistillode 5–6.5 mm long. Pistillate flowers 4.6–5 mm diam.; calyx 4.7–5.7 mm high, lobes 1.7–2 by 1–1.4 mm; disc glands absent; ovary 1.8–2.8 by 1.6–2.2 mm, densely hairy; stigma 0.5–0.8 mm long. Fruits globose, c. 4.8 by 4.1 cm, wall 3.5–3.8 mm thick; pedicel 1–2.5 cm long; column 2.5–2.7 cm long. Seeds c. 2.4 by 1.4 by 1 cm.

    Distribution — Tropical South America, from the Guianas to Amazonia. Once cultivated in the Botanical Garden of Bogor (former called Buitenzorg) in Indonesia.

    Habitat & Ecology — Flowering: August to October; fruiting: November to December.

3. Hevea pauciflora (Spruce ex Benth.) Müll.Arg.

    Hevea pauciflora (Spruce ex Benth.) Müll.Arg., Linnaea 34 (1865) 203; in A.DC., Prodr. 15, 2 (1866) 717; Pax in Engl., Pflanzenr. IV.147.i (1910) 126; Ducke, Arq. Inst. Biol. Veg. 2 (1935) 224; R.E.Schult., Bot. Mus. Leafl. 15 (1952) 255; Bot. Rev. 36 (1970) 223; Regnum Veg. 71 (1970) 229; Bot. Mus. Leafl. 25 (1977) 243; Hoang Van Sam & Welzen, Blumea 49 (2004) 437. — Siphonia pauciflora Spruce ex Benth., J. Bot. (Hooker) 6 (1854) 370. — Type: Spruce 2691 (K n.v.), Brazil, Rio Uaupés.

For further synonyms see the various publications of Schultes (esp. 1952, 1970 & 1970).

Tree, up to 30 m high. Bark dark brown, c. 1 mm thick; inner bark light brown, c. 1.5 cm thick; wood white. Stipules not seen. Leaves: petiole 5–21.4 cm long; petiolules 3–10 mm long; leaflets obovate, 6.7–24.5 by 2.9–10.2 cm, length/width ratio 2.3–2.4, reclined to semi-erect, base attenuate to cuneate, apex acuminate to cuspidate, upper surface glabrous, lower surface subglabrous, venation pinnate, flat above, raised beneath, nerves 10–23 till apex. Inflorescences up to 37.4 cm long, hairy, branches up to 11.5 cm long; bracts very small. Staminate flowers 4–5.2 mm diam., yellowish, sweet scented; pedicel 3–24 mm long; calyx 4.7–5.4 mm long, lobes 2.8–3.4 by 1.2–1.5 mm; androphore 2.5–2.8 mm long, stamens 10, united in two layers, anthers, 0.7–0.8 by c. 0.2 mm; disc glands present; pistillode 5.6–7.9 mm long. Pistillate flowers 5–5.4 mm diam.; calyx 6.5–7.2 mm high, lobes 4.1–4.5 by 1–1.5 mm; disc glands 1–1.2 mm high; ovary 2.2–2.5 by 2–2.2 mm, hairy; stigmas 0.2–0.3 mm long. Fruits 4–4.5 by 3.8–4.1 cm high, wall 3.5–4 mm thick; pedicel 0.8–2 cm long; column 2.5–2.8 cm long. Seeds 2.2–2.3 by 1.7–1.9 by 1.5–1.6 cm.

    Distribution — South America: North Amazonia and British Guyana. Once cultivated in the Botanical Garden of Bogor (former called Buitenzorg) in Indonesia.

    Habitat & Ecology — Flowering: July to November; fruiting: October to January.