Habit and leaf form. Herbs. Annual, or perennial. Leaves basal, or cauline. Stem internodes solid. To 0.1–0.8 m high. Helophytic. Leaves medium-sized; alternate; spiral; ‘herbaceous’; petiolate (lower leaves), or subsessile to sessile; non-sheathing; foetid (when crushed); simple; epulvinate. Leaf blades dissected, or entire; pinnately veined; cross-venulate. Leaves without stipules. Leaf blade margins entire, or serrate, or dentate. Leaves without a persistent basal meristem. Leaf anatomy. Hairs present, or absent; glandular hairs absent; complex hairs absent. Branched hairs absent. Extra-floral nectaries absent.
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite.
Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; in racemes, or in corymbs. The terminal inflorescence unit racemose. Flowers pedicellate; ebracteate; ebracteolate; small to medium-sized; fragrant; regular; 2 merous; cyclic. Floral receptacle developing a gynophore, or with neither androphore nor gynophore. Free hypanthium absent. Hypogynous disk present; of separate members. Nectariferous glands 4. Perianth with distinct calyx and corolla; 8; 3 -whorled (K 2+2, C 4). Calyx present; 4; 2 -whorled; polysepalous; somewhat spreading to erect; decussate; regular. Corolla present; 4; 1 -whorled; alternating with the calyx; polypetalous; imbricate, or contorted; regular; veins often distinctly coloured but not purple. Petals clawed. Androecial members definite in number. Androecium 6. Androecial members branched (in that the inner whorl of 4 is derived from only 2 primordia); free of the perianth; markedly unequal; free of one another; 2 -whorled (2+4). Androecium exclusively of fertile stamens. Stamens 6 (2 outer, 4 inner); tetradynamous; all more or less similar in shape; hypogynous, on receptacle, outer stamens lateral. Filaments not appendiculate. Anthers basifixed; non-versatile; dehiscing via longitudinal slits; introrse; unilocular to bilocular; tetrasporangiate. Pollen shed as single grains. Gynoecium 2 carpelled. The pistil 2 celled. Gynoecium syncarpous; eu-syncarpous; superior. Ovary plurilocular; 2 locular. Locules secondarily divided by ‘false septa’. Gynoecium transverse. Ovary sessile to stipitate. Gynoecium stylate. Styles 1; apical. Stigmas 1 (or 2); 1 - lobed; capitate. Placentation parietal. Ovules 20–50 per locule; with ventral raphe; non-arillate; anatropous.
Fruit and seed features. Fruit 20–60 mm long; non-fleshy; dehiscent; a siliqua. Capsules valvular. Fruit 2 celled; 30–100 seeded (‘many’). Seeds 20–50 per locule (‘many’). Seed rows per locule 2. Seeds scantily endospermic, or non-endospermic; not mucous; small to medium sized; wingless (ovoid). Embryo well differentiated. Cotyledons 2; folded; incumbent; conduplicate. Embryo bent.
Physiology, biochemistry. Mustard-oils present.
Special features. Fruit body distinctly differentiated into valve and beak regions. Beak seedless. Replum present and complete. Fruit terete; compressed parallel with the septum. The inner (lateral) pair of sepals somewhat saccate basally for nectar storage, or not noticeably saccate. Petals not peculiarly elongated as in Stenopetalum. Nectariferous glands lateral and median. Valves of the fruit neither winged nor keeled; conspicuously longitudinally veined; longitudinally 1 veined.
Etymology. From the Greek "double" and "an arrangement of anything" e.g. a single rank of soldiers; refers to the double row of seeds.
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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/