Cytisus Desf.

Scientific Description

Family Papilionaceae. Genisteae.

Habit and leaf form. Small trees, or shrubs (usually with with long- and short-shoots). ‘Normal’ plants, or switch-plants (often); the switch forms with the principal photosynthesizing function transferred to stems (the older branches often green and long persistent). Leaves well developed, or much reduced. Plants spiny (rarely), or unarmed. The spines axial. Mesophytic, or xerophytic. Heterophyllous, or not heterophyllous. Leaves minute to medium-sized; fasciculate, or not fasciculate; alternate (usually), or opposite; spiral, or distichous; when opposite, decussate; with blades, or bladeless; ‘herbaceous’, or leathery, or membranous, or modified into spines; not imbricate; petiolate, or subsessile, or sessile; non-sheathing; simple, or compound (usually); pulvinate to epulvinate (the pulvini often fused to the branch and persistent); when compound, unifoliolate, or ternate. Leaves when trifoliolate, palmately trifoliolate. Leaflets 1, or 3; not stipellate; pulvinate, or epulvinate. Leaf blades dorsiventral, or isobilateral, or centric. Leaves with stipules, or without stipules. Stipules when present, intrapetiolar; adnate to the petiole (and often fused to the branch), or free of the petiole; free of one another; scaly, or leafy, or spiny; caducous, or persistent. Leaves without a persistent basal meristem. Leaf anatomy. Complex hairs present, or absent. Branched hairs present (biramous), or absent. Stem anatomy. Nodes tri-lacunar, or penta-lacunar. Secondary thickening developing from a conventional cambial ring.

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Entomophilous.

Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; not crowded at the stem bases; in racemes, or in heads, or in umbels. Inflorescences simple, or compound (sometimes aggregated to for pseudoracemes). The terminal inflorescence unit cymose, or racemose. Inflorescences terminal, or axillary. Flowers bracteate, or ebracteate. Bracts deciduous. Flowers bracteolate, or ebracteolate. Bracteoles deciduous. Bracteoles not adnate to the receptacle. Flowers small to large; very irregular; zygomorphic. The floral asymmetry involving the perianth and involving the androecium. Flowers papilionaceous (imbricate-descending, with the posterior petal outside and forming a ‘standard’); basically 5 merous. Floral receptacle developing a gynophore, or with neither androphore nor gynophore. Free hypanthium present, or absent. Perianth with distinct calyx and corolla; 10; 2 -whorled; isomerous. Calyx present; 5; 1 -whorled; gamosepalous; lobed. Calyx lobes markedly shorter than the tube. Calyx imbricate, or valvate; exceeded by the corolla; campanulate; bilabiate (the posterior lip 2-toothed, the anterior 3-toothed); persistent; non-accrescent; with the median member anterior. Epicalyx absent. Corolla present; 5; 1 -whorled; appendiculate, or not appendiculate. Standard not appendaged. Corolla partially gamopetalous. 2 of the petals joined (the two ventral petals connivent to form the ‘keel’, the tips of the wings free). The joined petals anterior. The wings of the corolla free from the keel; not laterally spurred. Standard ‘normally’ developed. Keel oblong-falcate to semi-circular, always curved beneath, usually glabrous; not long-acuminate/beaked (at the most, only slightly so); neither coiled nor spiralled; not bent and beaked. Corolla imbricate (descending); usually with contrasting markings; white, or cream, or yellow, or yellow and red, or purple to blue (rarely?); deciduous; non-accrescent. Petals clawed (the claws free). Androecial members definite in number. Androecium 10. Androecial sequence determinable, or not determinable. Androecial members free of the perianth; all equal, or markedly unequal; coherent (the filaments united basally into a closed tube); 1 - adelphous. The staminal tube adnate to the keel petals, or free from the keel petals. Androecial members 1 -whorled. Androecium exclusively of fertile stamens. Stamens 10; distinctly dissimilar in shape (the anthers alternately long basifixed, short dorsifixed); diplostemonous; both opposite and alternating with the corolla members. Anthers separate from one another, or connivent; dimorphic (long-basifixed, short-dorsifixed); alternately dorsifixed and basifixed; alternately versatile and non-versatile; dehiscing via pores, or dehiscing via longitudinal slits; latrorse, or introrse; tetrasporangiate. Pollen shed as single grains. Gynoecium 1 carpelled. The pistil 1 celled. Carpels reduced in number relative to the perianth. Gynoecium monomerous; of one carpel; superior. Carpel stylate; apically stigmatic. Style upwardly curved, or sigmoid (rarely ‘convolute’). Style glabrous. Stigmatic tissue terminal, or oblique. Carpel 3–25 ovuled (i.e. to ‘many’). Placentation marginal (along the ventral suture). Gynoecium median (the placenta posterior, on the ventral suture). Ovary sessile to stipitate. Stigmas capitate, or punctiform. Ovules pendulous to ascending; biseriate; arillate; anatropous, or campylotropous to amphitropous, or hemianatropous.

Fruit and seed features. Fruit stipitate to sessile; non-fleshy; hairy, or not hairy. The fruiting carpel dehiscent; a legume. Pods somewhat elongated, or much elongated (usually oblong or linear-oblong); not triangular; straight, or curved; becoming inflated, or not becoming inflated; more or less flat; regularly constricted between adjacent seeds, or irregularly constricted, or not constricted between the seeds; not transversely septate (rarely ‘subseptate’); wingless. Valves of the dehisced pod twisted, or not twisted. Fruit 1 celled; elastically dehiscent, or passively dehiscent. Dispersal unit the seed. Fruit 2–25 seeded. Seeds ovate-oblong or obliquely elliptic; endospermic, or non-endospermic; not mucous; small to medium sized; arillate (often), or non-arillate. Cotyledons 2; if radicle flexed, accumbent. Embryo chlorophyllous; straight, or curved, or bent. Testa non-operculate. Micropyle zigzag, or not zigzag. Seedling. Germination phanerocotylar, or cryptocotylar.

Physiology, biochemistry. Nitrogen-fixing root nodules present. Aluminium accumulation not found. Photosynthetic pathway: C₃.

Geography, cytology, number of species. Adventive. 2n=(22, 24, 46) 48 (92, 96). A genus of 33 species; 1 species in Western Australia.