Tersonia Moq.
Prodr. 13(2):5, 40. (1849)

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Name Status: Current

Scientific Description
J. Gathe and Leslie Watson, Friday 3 October 2008

Common name. Button Creeper. Family Gyrostemonaceae.

Habit and leaf form. Shrubs, or herbs. Plants somewhat succulent. Annual, or biennial. Leaves cauline. Young stems cylindrical. Stem internodes solid. Xerophytic. Leaves small, or medium-sized; alternate; spiral; fleshy, or ‘herbaceous’ to leathery; petiolate to sessile; non-sheathing; simple; epulvinate. Leaf blades entire; solid (usually semi-terete); linear, or lanceolate, or oblanceolate, or oblanceolate, or ovate; obovate (rarely), or linear; one-veined, or pinnately veined. Leaves with stipules (small). Leaf blade margins entire. Leaves without a persistent basal meristem. Leaf anatomy. Hairs absent. Extra-floral nectaries absent. Stem anatomy. Secondary thickening developing from a conventional cambial ring.

Reproductive type, pollination. Fertile flowers functionally male, or functionally female. Unisexual flowers present. Plants dioecious. Female flowers without staminodes. Male flowers without pistillodes.

Inflorescence and flower features. Flowers solitary (female flowers), or aggregated in ‘inflorescences’ (male flowers); in racemes, or in spikes (interrupted). The terminal inflorescence unit racemose. Inflorescences terminal (male raceme, spike), or axillary (male raceme, solitary female); racemose or spicate. Flowers pedicellate (in male and female flowers), or sessile to subsessile (in male flowers); ebracteate; bracteolate (small); small; regular; cyclic. Perianth sepaline; 4–5 (if segments detectable); 1 -whorled; joined. Calyx present; 4, or 5 (when lobed); 1 -whorled; gamosepalous; blunt-lobed (shallowly in male flowers); regular; persistent. Corolla absent. Fertile stamens present, or absent. Androecial members definite in number. Androecium 8–17. Androecial sequence determinable, or not determinable. 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 8–17; all more or less similar in shape; polystemonous; in 1 whorl around the central disc on the edge of the expanded receptacle; filantherous (almost sessile). Anthers dehiscing via longitudinal slits; introrse. Fertile gynoecium present, or absent. Gynoecium 15–20 carpelled. The pistil 15–20 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 plurilocular; 15–20 locular; sessile. Gynoecium stylate. Styles 15–20; apical. Stigmas 15–20. Placentation axile. Ovules 1 per locule; apotropous; arillate; anatropous.

Fruit and seed features. Fruit non-fleshy (somewhat woody); interpretable as an aggregate (if seen as resulting from more or less ‘free’ carpels). The fruiting carpels coalescing into a secondary syncarp to not coalescing. Fruit indehiscent; 15–20 celled; 15–20 seeded. Seeds copiously endospermic. Endosperm oily. Embryo well differentiated. Cotyledons 2. Embryo curved.

Physiology, biochemistry. Mustard-oils present.

Etymology. From the Greek for "to be dried up"; refers to the absence of albumen in the fruit.

Taxonomic Literature

Blackall, William E.; Grieve, Brian J. (1988). How to know Western Australian wildflowers : a key to the flora of the extratropical regions of Western Australia. Part I : Dicotyledons (Casuarinaceae to Chenopodiaceae). University of W.A. Press. Perth.

Marchant, N. G.; Wheeler, J. R.; Rye, B. L.; Bennett, E. M.; Lander, N. S.; Macfarlane, T. D.; Western Australian Herbarium (1987). Flora of the Perth region. Part one. Western Australian Herbarium. Perth.