Family Gyrostemonaceae

Gyrostemonaceae Endl.

Habit and leaf form. Trees, or shrubs (or undershrubs). Plants non-succulent. Xerophytic. Leaves small, or medium-sized; alternate; spiral; fleshy (often), or ‘herbaceous’ to leathery; petiolate to sessile; non-sheathing; simple; epulvinate. Lamina entire; linear, or lanceolate, or oblanceolate, or oblanceolate, or ovate; one-veined, or pinnately veined. Leaves stipulate (the stipules minute), or exstipulate; without a persistent basal meristem.

Leaf anatomy. Lamina without secretory cavities.

Stem anatomy. Secretory cavities absent. Internal phloem absent. Secondary thickening developing from a conventional cambial ring. ‘Included’ phloem absent. Vessel end-walls simple. Wood partially storied (VPI). Sieve-tube plastids S-type.

Reproductive type, pollination. Fertile flowers functionally male, or functionally female, or functionally male and functionally female. Plants dioecious (mostly), or monoecious.

Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’; in racemes and in spikes. The ultimate inflorescence unit racemose. Inflorescences racemose or spicate. Flowers bracteolate; small; regular; cyclic.

Perianth sepaline; 4–5 (if segments detectable); joined (discoid or cupular, entire or more or less lobed); 1 whorled. Calyx 4, or 5 (when lobed); 1 whorled; gamosepalous; entire, or lobulate, or blunt-lobed; regular; persistent.

Androecium 6–100 (i.e., to ‘many’, arising from the edge of the flat or convex receptacle). Androecial members when in more than one cycle, maturing centripetally; free of the perianth; all equal; free of one another; 1–5 whorled. Androecium exclusively of fertile stamens. Stamens 6–100 (to ‘many’); commonly polystemonous; filantherous (shortly), or with sessile anthers. Anthers dehiscing via longitudinal slits; introrse; unappendaged. Pollen grains aperturate; 3 aperturate; colpate, or colporate (?).

Gynoecium (2–)5–100 carpelled (i.e. to ‘many’). The pistil when syncarpous, (2–)5–25 celled. Gynoecium apocarpous to syncarpous; semicarpous to synovarious (the carpels adnate to the central column, forming a compound ovary); superior. Carpel non-stylate to stylate; apically stigmatic; if considered apocarpous, 1 ovuled. Placentation marginal. Ovary if viewed as syncarpous, (2–)5–25 locular (i.e. as many locules as carpels). Locules without ‘false septa’. Gynoecium stylate, or non-stylate. Styles when present, (2–)5–25 (but very short); apical. Stigmas (2–)5–25 (the ring of stigmas forming a corona). Placentation axile. Ovules 1 per locule; apotropous; arillate; anatropous.

Fruit fleshy (often, at first), or non-fleshy (finally); interpretable as an aggregate (if seen as resulting from more or less ‘free’ carpels), or not an aggregate. The fruiting carpels coalescing into a secondary syncarp to not coalescing. Fruit a schizocarp (the carpels separating from the central column), or dehiscent and a schizocarp. Mericarps 2–25; comprising follicles, or comprising ‘legumes’ (the carpels dehiscing dorsally, ventrally or both). Seeds copiously endospermic. Endosperm oily. Embryo well differentiated. Cotyledons 2; flat. Embryo curved.

Physiology, biochemistry. Mustard-oils present. Cyanogenic, or not cyanogenic. Iridoids not detected. Proanthocyanidins absent. Ellagic acid absent. Betalains absent. Aluminium accumulation not found.

Geography, cytology. Temperate to tropical. Australia. X = 14, 15.

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Violiflorae; Capparales. Cronquist’s Subclass Dilleniidae; Batales. APG 3 core angiosperms; core eudicot; Superorder Rosanae; malvid; Order Brassicales.

Species 16. Genera 5; Codonocarpus, Cypselocarpus, (Didymotheca), Gyrostemon, Tersonia, Walteranthus.

Illustrations.
• Gyrostemon (carpel and fruit).