Common name. Buckthorn. Family Rhamnaceae.
Habit and leaf form. Trees, or shrubs; evergreen, or deciduous. ‘Normal’ plants. Leaves well developed. Plants with roots; non-succulent; spiny, or unarmed; autotrophic. To 1–4 m high (in Australia). Self supporting. Not heterophyllous. Leaves medium-sized; not fasciculate; alternate (in Australia, R. alaternus); with blades; petiolate; with ‘normal’ orientation; simple; not peltate. Leaf blades entire; flat; elliptic (to broadly so, in Australia). Mature leaf blades adaxially glabrous; abaxially glabrous. Leaves with stipules. Stipules small scaly, or spiny; caducous, or persistent (rarely). Leaf blade margins serrate (in Australia); flat. Leaf anatomy. Hairs absent.
Reproductive type, pollination. Fertile flowers functionally male, or functionally female. Unisexual flowers present. Plants monoecious, or dioecious.
Inflorescence and flower features. Flowers aggregated in ‘inflorescences’. Inflorescence many-flowered, or few-flowered. Flowers in racemes (in Australia). The terminal inflorescence unit racemose. Inflorescences axillary (in Australia). Flowers pedicellate; bracteate; minute; regular; 4 merous, or 5 merous; cyclic. Perianth with distinct calyx and corolla, or sequentially intergrading from sepals to petals (rarely); 8–10, or 4–5; 2 -whorled, or 1 -whorled; isomerous. Calyx present; 4, or 5; 1 -whorled; gamosepalous; valvate; regular. Calyx lobes ovate to triangular. Epicalyx absent. Corolla present, or absent; 5, or 4; 1 -whorled; alternating with the calyx; polypetalous; regular; deciduous. Petals oblong. Androecium present, or absent (staminodes only in female flowers). Fertile stamens present, or absent. Androecial members definite in number. Androecium 5, or 4. Androecial members adnate (to the base of the sepals); free of the gynoecium; free of one another; 1 -whorled. Androecium exclusively of fertile stamens. Stamens 5, or 4; all more or less similar in shape; isomerous with the perianth; alternisepalous; filantherous. Anthers separate from one another; dehiscing via longitudinal slits; bilocular; tetrasporangiate. Fertile gynoecium present, or absent (ovary and style rudimentary in male flowers). Gynoecium 2–4 carpelled. The pistil 1 celled. Carpels reduced in number relative to the perianth, or isomerous with the perianth (rarely). Gynoecium syncarpous; synovarious, or synstylovarious, or eu-syncarpous; inferior, or partly inferior, or superior (rarely). Ovary plurilocular; 1–4 locular. Ovary summit glabrous. Gynoecium stylate. Styles 1; deeply 3 branched; apical. Stigmas 1 - lobed. Ovules 1 per locule; ascending; anatropous.
Fruit and seed features. Fruit aerial; 5–6 mm long; dehiscent, or indehiscent; a drupe. Dispersal unit the seed. Seeds 1 per locule.
Geography, cytology, number of species. Adventive. Not endemic to Australia. Australian states and territories: Western Australia, South Australia, Queensland, New South Wales, and Victoria. South-West Botanical Province. A genus of ca 100 species; 1 species in Western Australia; R. alaternus L.; 0 endemic to Western Australia.
Etymology. From the Greek name of a shrub.
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Western Australian Herbarium (1998–). FloraBase—the Western Australian Flora. Department of Biodiversity, Conservation and Attractions. https://florabase.dpaw.wa.gov.au/