Family Scyphostegiaceae

Scyphostegiaceae Hutch.

~ Salicaceae sensu lato

Habit and leaf form. Small trees. Leaves alternate; distichous; shortly petiolate; simple. Lamina entire; pinnately veined; cross-venulate (with ‘rhamnaceous’, close-transverse tertiary venation). Leaves stipulate. Stipules caducous (very small). Lamina margins serrate, or dentate.

Leaf anatomy. Stomata present; mainly confined to one surface (abaxial); paracytic. Hairs seemingly absent.

Lamina dorsiventral. The mesophyll containing calcium oxalate crystals. The mesophyll crystals druses.

Stem anatomy. Young stems tetragonal. Cork cambium present; initially superficial. Nodes tri-lacunar. Secondary thickening developing from a conventional cambial ring. The secondary phloem not stratified. ‘Included’ phloem absent. Xylem with fibre tracheids (finely, transversely septate); with libriform fibres; with vessels. Vessel end-walls very oblique; simple. Primary medullary rays narrow. Wood parenchyma paratracheal (but represented only by occasional cells — almost ‘absent’).

Reproductive type, pollination. Fertile flowers functionally male, or functionally female. Plants dioecious.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in racemes, in spikes, and in panicles. Inflorescences terminal; panicles of racemosely arranged spikes or racemes, the lower branches subtended by foliage leaves. Flowers bracteate (each raceme with a series of overlapping, nested, tubular bracts, each subtending a single flower, and the latter expanding one at a time); regular; 3 merous (exclusive of the gynoecium in female flowers); cyclic. Free hypanthium present (tubular). Hypogynous disk present, or absent (depending on interpretation — the male flowers with curious stublike structures on the same radius as the stamens); if considered present, extrastaminal; of separate members (in the form of three seemingly glandular, stublike structures, on the same radius as the inner perianth members and stamens).

Perianth with distinct calyx and corolla (more or less, at least in the female flowers), or of ‘tepals’ (at least in male flowers); 6; free; 1 whorled (3+3); isomerous. Calyx if recognised as such, 3; of female flowers, 1 whorled; polysepalous. Corolla of female flowers, 3; 1 whorled; polypetalous.

Androecium of male flowers, 3, or 6 (if the stublike structures in front of the three inner perianth segments and stamens are taken as androecial). Androecial members free of the perianth; all equal, or markedly unequal (depending on interpretation); completely coherent; 1 adelphous (fully united into a column, back to back); 1 whorled, or 2 whorled (depending on interpetation). Androecium exclusively of fertile stamens, or including staminodes. Staminodes (if the stublike structures are so interpreted), 3; external to the fertile stamens. Stamens 3; isomerous with the perianth; alternisepalous. Anthers dehiscing via longitudinal slits; extrorse; bilocular; tetrasporangiate; appendaged. The anther appendages apical (by a clavate prolongtion of the common connective). Pollen shed as single grains. Pollen grains aperturate; 3 aperturate; colpate.

Gynoecium 8–13 carpelled. Carpels increased in number relative to the perianth. The pistil 1 celled, or 8–13 celled (above). Gynoecium syncarpous; eu-syncarpous; superior. Ovary 1 locular (at least below, but partitioned near the summit); sessile. Gynoecium essentially non-stylate. Stigmas 1 (this thick, discoid, centrally imperfect, with as many radiating ridges as carpels). Placentation basal (usually so described), or free central (perhaps better, the ovules being ‘on a somewhat convex receptacle’). Ovules in the single cavity 30–100 (‘many’); conspicuously funicled (pedestaled); ascending; arillate; strongly anatropous (with the raphe external); bitegmic; crassinucellate. Outer integument contributing to the micropyle. Embryo-sac development more or less Polygonum-type. Endosperm formation nuclear (at first), or cellular (subsequently).

Fruit fleshy; dehiscent; a capsule. Capsules loculicidal and valvular (opening from the top by reflexing valves which separate at the midveins of the carpels). Seeds scantily endospermic. Endosperm oily. Perisperm present (in a very thin layer). Embryo well differentiated (large). Cotyledons 2. Embryo straight.

Seedling. Germination phanerocotylar.

Physiology, biochemistry. Aluminium accumulation not found.

Geography, cytology. Paleotropical. Tropical. Borneo. N = 9.

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Violiflorae; Violales. Cronquist’s Subclass Dilleniidae; Violales. APG 3 core angiosperms; core eudicot; Superorder Rosanae; fabid; Order Malpighiales (as a synonym of Salicaceae).

Species 1. Genera 1; only genus, Scyphostegia.

Van Heel 1967; Metcalfe 1956.