Family Aralidiaceae

Aralidiaceae Philipson and Stone

Habit and leaf form. Small, Artocarpus-like trees, or shrubs. To 15–17 m high. Pachycaul, or leptocaul (more or less, with age). Leaves evergreen to deciduous (with ‘intermittent’ leaf fall); alternate; spiral; flat; ‘herbaceous’, or leathery (?); petiolate; sheathing. Leaf sheaths not tubular; with free margins. Leaves simple. Lamina dissected; pinnatifid; pinnately veined; cross-venulate. Leaves exstipulate (though the petiole margins are spread). Lamina margins coarsely dentate, or entire; flat.

General anatomy. Plants with ‘crystal sand’ (in epidermal and subepidermal leaf tissues, and in the stem).

Leaf anatomy. Stomata present; on both surfaces; anisocytic. Hairs present; eglandular and glandular; unicellular and multicellular. Unicellular hairs unbranched. Multicellular hairs uniseriate; unbranched. Complex hairs absent.

Adaxial hypodermis absent. Lamina dorsiventral; without secretory cavities. Main veins embedded.

Stem anatomy. Secretory cavities absent. Cork cambium present; initially superficial. Nodes multilacunar. Cortical bundles present (reflecting the multilacunar nodes). Secondary thickening developing from a conventional cambial ring. Xylem without fibre tracheids; with libriform fibres (frequently septate); with vessels. Vessel end-walls oblique; scalariform (with numerous bars). Wood diffuse porous; parenchyma paratracheal. Pith heterogeneous (with sclereids).

Reproductive type, pollination. Fertile flowers functionally male, or functionally female. Plants dioecious. Female flowers with staminodes (five). Gynoecium of male flowers absent.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in panicles. The ultimate inflorescence unit cymose. Inflorescences terminal; (both male and female) paniculate, the male plants with panicles of cymules of tiny flowers. Flowers bracteolate; regular; (male and female) 5 merous. Floral receptacle with neither androphore nor gynophore. Free hypanthium present, or absent (?).

Perianth with distinct calyx and corolla; 10; 2 whorled; isomerous. Calyx 5; 1 whorled; polysepalous, or gamosepalous (?); lobulate, or blunt-lobed; regular; persistent (?); non-accrescent; open in bud (?). Corolla 5; 1 whorled; polypetalous; slightly imbricate; regular.

Androecium 5. Androecial members free of the perianth; all equal (?); free of one another; 1 whorled. Androecium of male flowers, exclusively of fertile stamens. Stamens 5; isomerous with the perianth; oppositisepalous (?); filantherous. Anthers dorsifixed; dehiscing via longitudinal slits (?). Pollen grains aperturate; 3 aperturate; colporate.

Gynoecium 3(–4) carpelled (but pseudomonomerous, with 2(–3) locules aborting). Carpels reduced in number relative to the perianth. The pistil 1 celled. Gynoecium syncarpous (with 2(–3) locules aborting); synovarious (with 3(–4) stylopodia and diverging styles); inferior. Ovary 1 locular (with the others aborting almost without trace). Epigynous disk present (of stylopodia). Gynoecium stylate. Styles 3(–4); free. Stigmas 3(–4). Placentation apical. Ovules differentiated; in the single cavity 1; funicled; pendulous; apotropous; with dorsal raphe; arillate; anatropous; unitegmic; tenuinucellate (the nucellus disintegrating by the time the sac is mature, save for a pedestal below it). Endothelium not differentiated (?). Embryo-sac development Polygonum-type (from a linear tetrad).

Fruit fleshy; indehiscent; a drupe (ovoid, the fleshy mesocarp about 5 mm thick). The drupes with one stone. Fruit 1 seeded. Seeds endospermic. Endosperm ruminate. Cotyledons 2. Embryo small, at the micropylar end.

Physiology, biochemistry. Iridoids detected; ‘Route I’ type (cf. Griselinia in structure). Arthroquinones not detected. Verbascosides detected (caffeic acid and unidentified derivatives — Bate-Smith in Philipson et al. 1980). Proanthocyanidins absent. Flavonols more or less absent (or traces of kaempferol). Ellagic acid absent (only caffeic acid and its derivatives found). C3. Anatomy non-C4 type.

Geography, cytology. Paleotropical. Tropical. Thailand, Malaysia, Singapore, Sumatra, Anambas, Borneo.

Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Araliiflorae (re-assigned); Araliales. Cronquist’s Subclass Rosidae; Cornales. APG (1998) Eudicot; core Eudicot; Asterid; Euasterid II. APG 3 (2009) Order: Apiales.

Species 1. Genera 1; only genus, Aralidium.

Philipson, Stone, Butterfield, Tseng, Jensen, Nielsen, Bate-Smith and Fairbrothers (1980). A genus on the Crassinucelli-Tenuinucelli borderline. The wood conforms with Araliaceae, but absence of secretory cavities, ovule orientation, iridoids, etc., seem cornaceous. The pollen details are said to differ from both. rbcL sequence comparisons, however, seem to have settled the question in favour of Araliiflorae (cf. Backlund and Bremer, 1997).

Support our developers