Euphorbiaceae

Homalanthus A.Juss.

First published in Euphorb. Gen.: 50 (1824), nom. cons.
This genus is accepted
The native range of this genus is Tropical Asia to Pacific.

Descriptions

Timothy M. A. Utteridge and Laura V. S. Jennings (2022). Trees of New Guinea. Kew Publishing. Royal Botanic Gardens, Kew

Distribution
A small genus of approximately 20 species throughout Malesia to Australia, New Caledonia, and the Pacific islands; six species in New Guinea (three endemic to the mainland, and Homalanthus trivalvis Airy Shaw currently only known from Bougainville and the Solomon Islands).
Morphology General
Latex present in all parts
Morphology General Indumentum
Indumentum often absent, consisting of simple, multicellular hairs where present
Morphology Leaves Stipules
Stipules relatively large, enclosing leaf buds and inflorescences, caducous
Morphology Leaves
Leaves alternate, simple, sometimes distinctly peltate, margins entire, lower surface usually whitish, penninerved, glands present lower surface in all species either near the margin, midrib or petiole, basal pair often enlarged; petiole present, glands absent or with less or apically with 1 or 2 or a cluster of apical glands
Morphology General Habit
Plants monoecious. Inflorescences terminal, appearing racemose, unbranched Trees to 20 m (in New Guinea)
Morphology Reproductive morphology Flowers
Flowers lacking petals and disk Staminate flowers: pedicel present, articulate; calyx with 1–2 free lobes; stamens 4–50, free, filaments nearly as long as anthers; pistillode absent
Morphology Reproductive morphology Flowers Gynoecium Pistil
Pistillate flowers: pedicel present, not articulate, elongating in fruit; calyx of 1–3 free lobes, persistent to caducous, glands absent or with basal glands; staminodes absent; ovary 2- or 3-locular, style very short to distinct, persistent, stigma longer than wide, usually recurved, undivided or divided, with a gland on the lower side at the apex
Morphology Reproductive morphology Fruits
Fruit a woody capsule, 2- or 3-locular, sometimes with only 1 seed developed and then with lateral style. Seeds elliptic-ovoid, caruncle present.
Ecology
Found in a variety of variety of habitats, especially in disturbed areas and regenerating forest; from sea level up to subalpine forest at 3500 m.
Recognition
The genus can be recognised by the white latex in all parts, the simple, alternate and entire leaves with petioles having 1 to several glands at the apex, and the terminal unbranched inflorescences with the flowers having conspicuous bract-glands at the base. Several species have distinctly discolorous leaves being pale or very glaucous below, and may be tinged or coloured red when young.
[TONG]

Euphorbiaceae, A. R.-Smith. Flora of Tropical East Africa. 1987

Morphology General Habit
Monoecious or dioecious trees or shrubs with milky latex, commonly glabrous, rarely with a localized simple indumentum
Morphology Leaves
Leaves alternate, long-petiolate, stipulate, peltate or not, simple, usually entire, penninerved, with a pair of glands at the apex of the petiole; stipules readily caducous
Morphology Reproductive morphology Inflorescences
Inflorescences terminal or subterminal, pseudoracemose, solitary, usually bisexual, predominantly ♂ with 1 or more ♀ flowers at the base; ♂ bracts broad, with a pair of sessile glands at the base, 1–6-flowered, the lowest ones sometimes also each subtending a ♀ flower; ♀ bracts usually 1-flowered
Morphology Reproductive morphology Flowers
Male flowers pedicellate; sepals 1 or 2, if 2 then imbricate and vertically disposed, giving the flowers a compressed appearance; petals 0; disc 0; stamens 5–50, free, filaments very short, anthers basifixed, bilobate, longitudinally dehiscent; pistillode 0 Female flowers long-pedicellate; calyx-lobes 2–3, open, not compressed; petals 0; disc 0; ovary 2(–3)-locular, with 1 ovule per locule; styles 2(–3), connate at the base, undivided or sometimes bilobate or shortly bifid, straight, the adaxial stigmatic surface running the length of the arms, canaliculate and minutely papillulose, the abaxial surface glandular or not
sex Male
Male flowers pedicellate; sepals 1 or 2, if 2 then imbricate and vertically disposed, giving the flowers a compressed appearance; petals 0; disc 0; stamens 5–50, free, filaments very short, anthers basifixed, bilobate, longitudinally dehiscent; pistillode 0
sex Female
Female flowers long-pedicellate; calyx-lobes 2–3, open, not compressed; petals 0; disc 0; ovary 2(–3)-locular, with 1 ovule per locule; styles 2(–3), connate at the base, undivided or sometimes bilobate or shortly bifid, straight, the adaxial stigmatic surface running the length of the arms, canaliculate and minutely papillulose, the abaxial surface glandular or not
Morphology Reproductive morphology Fruits
Fruit 2(–3)-lobed, subindehiscent or tardily loculicidally dehiscent; endocarp thinly crustaceous; columella small, subpersistent
Morphology Reproductive morphology Seeds
Seeds ovoid-ellipsoid; endotesta crustaceous; caruncle fleshy, sometimes half enclosing the seed; cotyledons broad, flat.
[FTEA]

Sources

  • Flora of Tropical East Africa

    • Flora of Tropical East Africa
    • http://creativecommons.org/licenses/by-nc-sa/3.0

  • Herbarium Catalogue Specimens

  • Kew Backbone Distributions

    • The International Plant Names Index and World Checklist of Vascular Plants 2024. Published on the Internet at http://www.ipni.org and https://powo.science.kew.org/
    • © Copyright 2023 World Checklist of Vascular Plants. http://creativecommons.org/licenses/by/3.0

  • Kew Names and Taxonomic Backbone

    • The International Plant Names Index and World Checklist of Vascular Plants 2024. Published on the Internet at http://www.ipni.org and https://powo.science.kew.org/
    • © Copyright 2023 International Plant Names Index and World Checklist of Vascular Plants. http://creativecommons.org/licenses/by/3.0

  • Trees of New Guinea

    • Trees of New Guinea
    • http://creativecommons.org/licenses/by-nc-sa/3.0