Sphenostemon

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Sphenostemon

Description

Shrubs or small trees. Leaves simple coriaceous, exstipulate, almost entire to distinctly glandular-dentate, penninerved, scattered, subopposite to pseudo-whorled, articulate at base. Flowers bisexual, actinomorphic, the pedicel articulate at the base, all opening about simultaneously, white. Sepals 4, free, decussate, widely imbricate, mostly hooded, sometimes less convex, rounded, outer ones mostly ± saccate at base, and with prominent midrib. Petals free, 0 or 4 similar to the sepals but of more fleshy texture, all caducous at anthesis. Stamens 1-seriate, 4, 6, or 8-13, ± sessile, after being exposed appearing as a globular body, sometimes with a few (1-3) flimsy appressed persistent appendages added (? staminodes), at anthesis free and expanded; Ovary superior, sessile on a thickened receptacle, often with grooves from the pressure of the stamens in bud, ± fusiform or cylindric, capped by a fleshy, cap-shaped, sessile, slightly bisected stigma; Seed(s) 1 and having the shape of the fruit, or 2 and then plano-convex.

Distribution

Asia-Tropical:, Maluku (Maluku present); New Guinea presentpresent Australasia:, Queensland (Queensland present) Central Celebes: present Ceram: present East Malesia: present N. Queensland: present New Britain: present New Caledonia: present present New Ireland and adjacent isles: present
New Caledonia, N. Queensland and East Malesia: New Guinea (incl. also New Britain, New Ireland and adjacent isles), Moluccas (Ceram) and Central Celebes. Four species in New Caledonia, 1 in Queensland and 3 in New Guinea.

Morphology

The New Caledonian species differ from the others in having 4 petals; all of them have few stamens (4 or 6) and often subentire leaves. According to BAAS (1975) they are also distinct from the species of ser. Apetalae in their vegetative anatomy. As exposed in the introduction, the structure of the seed is different from that hitherto assumed as a pyrene with the bony tissue derived from the endocarp; or, as BAILEY (1956) assumed, from the testa. As a matter of fact the fleshy 'pericarp' is on its inside lined by an epidermis against the bony tissue. The bony tissue, continued inside by soft tissue, is again demarcated against the seed proper; the envelope of the seed is derived from the chalaza which, during development of the fruit, completely surrounds the seed. In ser. Apetalae the bony outer part of the pachychalaza extends ruminations in the soft part of it.
However, in the New Caledonian S. pachycladus of ser. Sphenostemon, the bony outer part of the pachychalaza is circular, without ruminations. Unfortunately I have not succeeded to obtain ripe fruit of the other three New Caledonian species to check the structure of their seed, although I found a slight indication of it in S. oppositifolius HURL.

Taxonomy

The differences found between the New Caledonian species and those from East Malesia and Queensland induce me to raise the series to the rank of section, as follows.

Citation

ENGLER - in E. & P., Nat. Pfl. Fam., ed. 2, 21. 1925: 197
GILG & SCHLTR - in Bot. Jahrb. 1923: f. 2
HATUS. - in Bot. Mag. Tokyo. 1952: 109
STEEN. - in Svensk Bot. Tidskr. 1955: 19
PERKINS, Gatt. Monim. 1925: f. 14
BAILL. - in Adansonia. 1875: 307
STEEN. - in Acta Bot. Neerl. 1952: f. 2