Sebastiania Spreng.

Scientific Description

Family Euphorbiaceae.

Habit and leaf form. Trees, or shrubs, or herbs; laticiferous (latex milky). Plants succulent, or non-succulent. Herbs annual, or perennial. Mesophytic, or xerophytic. Leaves small to medium-sized; alternate; spiral, or distichous; ‘herbaceous’, or leathery, or fleshy; petiolate; non-sheathing; gland-dotted, or not gland-dotted; simple. Leaf blades entire; pinnately veined. Leaves with stipules. Stipules in S. chamaelea small, triangular, ciliate; caducous, or persistent. Leaf blade margins often minutely serrulate. Leaves without a persistent basal meristem. Leaf anatomy. Urticating hairs present, or absent. Stem anatomy. Nodes tri-lacunar, or unilacunar. Secondary thickening developing from a conventional cambial ring, or anomalous; from a single cambial ring.

Reproductive type, pollination. Fertile flowers functionally male, or functionally female. Unisexual flowers present. Plants monoecious. The unisexual flowers aggregated in different parts of the same inflorescence (the male flowers in clusters along the axis and the female flowers solitary or a few at the base of the axis). Male flowers without pistillodes. Entomophilous.

Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; in spikes, or in racemes. Inflorescences terminal, or leaf-opposed. Flowers bracteate, or ebracteate; minute to small; regular. Floral receptacle developing an androphore, or with neither androphore nor gynophore (? stamens inserted on a central receptacle). Free hypanthium absent. Hypogynous disk absent. Perianth sepaline; 2, or 3; 1 -whorled. Calyx 2, or 3; 1 -whorled; polysepalous, or gamosepalous; regular. Fertile stamens present, or absent (female flowers). Androecium 2, or 3. Androecial members free of the perianth; free of one another. Androecium exclusively of fertile stamens. Stamens 2, or 3; isomerous with the perianth; erect in bud, or inflexed in bud. Anthers dehiscing via short slits; extrorse, or introrse; bisporangiate, or tetrasporangiate. Fertile gynoecium present, or absent (male flowers). Gynoecium 3 carpelled. The pistil 3 celled. Gynoecium syncarpous; synovarious, or synstylovarious (depending on interpretation of the partially fused styles); superior. Ovary plurilocular; 3 locular. Styles 3; free, or partially joined (shortly connate at the base); simple (linear); apical. Stigmas 3; dry type; papillate, or non-papillate; Group II type. Placentation axile, or apical. Ovules 1 per locule; pendulous; epitropous; with ventral raphe, or with dorsal raphe; arillate; orthotropous, or anatropous, or hemianatropous.

Fruit and seed features. Fruit non-fleshy; a schizocarp (with a central persistent axis; the capsule of S. chamaelea smooth except for 1-several conical processes on the abaxial surface of each mericarp). Mericarps 3. Fruit elastically dehiscent (schizocarpic capsules often splitting elastically), or passively dehiscent. Seeds 1 per mericarp. Seeds ovoid or obloid; endospermic. Endosperm oily. Seeds arillate. Cotyledons 2 (usually wider than the radicle). Embryo straight, or curved. Seedling. Germination phanerocotylar, or cryptocotylar.

Physiology, biochemistry. Mustard-oils present, or absent.

Geography, cytology, number of species. Native of Australia. Not endemic to Australia. Australian states and territories: Western Australia, Northern Territory, and Queensland. Northern Botanical Province and Eremaean Botanical Province.