~ Apocynaceae, Loganiaceae
Habit and leaf form. Trees and shrubs; non-laticiferous and without coloured juice. Plants non-succulent. Leaves evergreen; 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. Stomata present; anomocytic. Hairs present; eglandular and glandular (eglandular-unicellular and glandular-bicellular). Unicellular hairs unbranched. Complex hairs present, or absent; if present, capitate.
Lamina dorsiventral. Cystoliths present (adjoining the bases of the CaCO2-filled, unicellular hairs).
Reproductive type, pollination. Plants hermaphrodite; homostylous.
Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’ (in groups of 1–7, pedicellate). The ultimate inflorescence unit 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 dorsifixed (ovate, basally cordate); 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); without an indusium; 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, biochemistry. Iridoids not detected. Verbascosides detected. Cornoside 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 3 core angiosperms; core eudicot; Superorder Asteranae; lamiid; Order Lamiales.
Species 3. Genera 1; only genus, Plocosperma (including Lithophytum).
Leeuwenberg 1980, under Loganiaceae.