The families of flowering plants

L. Watson and M.J. Dallwitz

Plocospermataceae Hutch.

~ Apocynaceae, Loganiaceae.

Habit and leaf form. Trees and shrubs; non-laticiferous. Leaves persistent; small; (sub-) whorled, or opposite; leathery; shortly petiolate; not connate; simple. Lamina entire; oblong to ovate (sometimes emarginate). Leaves exstipulate. Lamina margins entire; slightly revolute.

Leaf anatomy. The leaf lamina dorsiventral. Stomata present; anomocytic. Hairs present; eglandular and glandular (eglandular-unicellular and glandular-bicellular). Unicellular hairs simple. Complex hairs present, or absent; if present, capitate. Cystoliths present (adjoining the bases of the CaCO2-filled, unicellular hairs). The mesophyll containing crystals. The crystals solitary-prismatic (styloids).

Reproductive type, pollination. Fertile flowers hermaphrodite. Plants hermaphrodite; homostylous.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’ (in groups of 1–7, pedicellate). The ultimate inflorescence units racemose. Inflorescences axillary; axillary, 1–7 flowered, racemose but the peduncle and axis very short. Flowers regular to somewhat irregular; slightly zygomorphic; 5–6 merous; cyclic; tetracyclic. Free hypanthium absent. Hypogynous disk absent.

Perianth with distinct calyx and corolla; 10, or 12; 2 whorled; isomerous. Calyx 5, or 6; 1 whorled; basally gamosepalous (small); blunt-lobed to toothed (the lobes lanceolate). Calyx lobes markedly longer than the tube. Calyx unequal but not bilabiate, or regular; persistent; non-accrescent; imbricate, or open in bud. Corolla 5, or 6; 1 whorled; gamopetalous (glabrous within); imbricate (the lobes broad, rounded); campanulate, or funnel-shaped; slightly unequal but not bilabiate, or regular; purple, or blue (or violet).

Androecium 5, or 6. Androecial members adnate (inserted in the corolla tube); all equal; free of one another; 1 whorled. Androecium exclusively of fertile stamens. Stamens 5, or 6; isomerous with the perianth; oppositisepalous; alternating with the corolla members; quite long filantherous. Anthers ovate, basally cordate, dorsifixed; dehiscing via longitudinal slits; more or less latrorse, or introrse. Pollen shed as single grains. Pollen grains aperturate; 3 aperturate; colporate.

Gynoecium 2 carpelled. Carpels reduced in number relative to the perianth. The pistil 1 celled. Gynoecium syncarpous; synovarious to synstylovarious (the style bifid above, its branches each apically two-lobed); superior. Ovary 1 locular; shortly stipitate. Gynoecium stylate. Styles 1–2 (deciduous); partially joined (i.e. the style bifid above); apical. Stigmas 4 (these small, clavate). Placentation basal to parietal, or parietal to apical (or both). Ovules in the single cavity 2, or 4; ascending, or pendulous and ascending (there being two parietal placentas, these with one or two basal-erect ovules each, or having two basal-erect ovules on one and two subapical-pendulous ovules on the other).

Fruit non-fleshy; dehiscent; a capsule (elongate-fusiform, ribbed). Capsules (two-) valvular (from the apex). Fruit 1 seeded (usually), or 1–4 seeded. Seeds sparsely endospermic (the endosperm fleshy); long-linear, subterete; apically conspicuously hairy (with a dense tuft). Embryo straight (linear).

Physiology, phytochemistry. Verbascosides detected. Cornoside detected. Iridoids not detected.

Geography, cytology. Neotropical. Sub-tropical to tropical. Mexico, Central America.

Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Lamiiflorae; Scrophulariales (?). Cronquist’s Subclass Asteridae; Gentianales. APG III core angiosperms; core eudicot; Superorder Asteranae; lamiid. APG IV Order Lamiales.

Species 1 (Plocosperma buxifolium). Genera 1; only genus, Plocosperma (including Lithophytum).

General remarks. Evidently close to Apocynaceae (q.v.), but seemingly differing in embryology and lack of iridoids, as well as no hypogynous disk, the basifixed, 4-locular anthers and aggregated pollen, and gynoecium details. See Leeuwenberg 1980, under Loganiaceae.

Illustrations. • Plocosperma buxifolium: Hook. Ic. Pl. 12 (1876). • Plocosperma buxifolium: Hutchinson.

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, genera included in each family, and classifications (Dahlgren; Dahlgren, Clifford, and Yeo; Cronquist; APG). See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 5th March 2018.’.