Arabidella (F.Muell.) O.E.Schulz

Scientific Description

Family Brassicaceae.

Habit and leaf form. Shrubs, or herbs. Herbs annual. Leaves cauline, or basal and cauline. Young stems cylindrical, or tetragonal (or fluted). Stem internodes solid. To 0.15–1 m high. Mesophytic and xerophytic. Leaves small to medium-sized; alternate; spiral; ‘herbaceous’; petiolate to sessile; non-sheathing; foetid, or without marked odour; simple; epulvinate. Leaf blades dissected to entire; pinnatifid, or much-divided (commonly bi-, tri- or multiply pinnate); one-veined, or pinnately veined. Leaves without stipules; 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 corymbs, or in racemes (lax to dense). The terminal inflorescence unit racemose. Flowers pedicellate; ebracteate; ebracteolate; minute to small; regular; 2 merous; cyclic. Floral receptacle developing a gynophore, or with neither androphore nor gynophore. Free hypanthium absent. Hypogynous disk present; of separate members to annular (glands confluent). Perianth with distinct calyx and corolla; 8; 3 -whorled (K 2+2, C 4). Calyx present; 4; 2 -whorled; polysepalous; almost erect, or spreading; decussate; regular. Corolla present; 4; 1 -whorled; alternating with the calyx; polypetalous; imbricate, or contorted; regular; white, or yellow. 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 (the outer pair shorter); free of one another; 2 -whorled (2+4). Androecium exclusively of fertile stamens. Stamens 6; tetradynamous; all more or less similar in shape; hypogynous, on receptacle. Filaments not appendiculate. Anthers basifixed; non-versatile; dehiscing via longitudinal slits; introrse; unilocular to bilocular; tetrasporangiate; appendaged, or unappendaged. 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; commissural; 1 - lobed, or 2 - lobed; capitate. Placentation parietal. Ovules (1–)3–50 per locule; with ventral raphe; non-arillate; anatropous.

Fruit and seed features. Fruit 4–33 mm long; non-fleshy; dehiscent; a siliqua. Capsules valvular. Fruit 2 celled. Seed rows per locule 1, or 2. Seeds scantily endospermic, or non-endospermic; mucous; compressed, or not compressed; small to medium sized; winged, or wingless. Embryo well differentiated. Cotyledons 2; incumbent. Embryo bent.

Physiology, biochemistry. Mustard-oils present.

Special features. Fruit body with no clear differentiation into valve and beak regions. Replum present and complete; broad. Fruit bilaterally compressed, or terete. The inner (lateral) pair of sepals not noticeably saccate. Petals not peculiarly elongated as in Stenopetalum. Nectariferous glands lateral and median (medians confluent with laterals). Valves of the fruit neither winged nor keeled; conspicuously longitudinally veined; longitudinally 1 veined.

Etymology. From genus Arabis, and the suffix for diminutive; indicating the smallness of the genus in comparison with Arabis.