Laburnum

Taxonomy

Laburnum P.C. Fabricius Enum. 228. 1759.

Subfamily: Faboideae.
Phylogenetic Number: 3.30.09.
Tribe: Genisteae.
Species Studied - Species in Genus: 2 studied; 2 in genus.

Description

Fruit: A legume; unilocular; 2–6 cm long; 0.7–1 cm wide; 0.15–0.4 cm thick; 2–9 times longer than wide; with deciduous androecial sheath, or persistent androecial sheath; with deciduous corolla; with deciduous calyx, or persistent calyx; with calyx shorter than fruit; without orifice formed by curving of fruit or fruit segments; straight, or curved (or slightly curved); not plicate; not twisted; symmetrical, or asymmetrical; linear, or oblong (narrowly); with both sutures nearly straight; not inflated; flattened, or compressed; without beak; long tapered at apex, or tapered at apex, or short tapered at apex; aligned with longitudinal axis of fruit, or oblique with longitudinal axis of fruit (slightly); long tapered at base, or tapered at base; aligned with longitudinal axis of fruit, or oblique with longitudinal axis of fruit (slightly); with the apex and base uniform in texture; coriaceous, or membranous, or ligneous; seed chambers externally visible; seed chambers with the raised seed chambers not torulose, or torulose; margin not constricted, or constricted; margin slightly constricted along both margins (hardly); margin without sulcus; margin plain; wing(s) absent; substipitate; with all layers dehiscing (tardily); splitting along suture(s). Dehiscence of valves along both sutures; apical and down; passive. Replum invisible. Epicarp dull; monochrome; dark to reddish brown, or tan; with surface texture uniform; glabrous, or pubescent and indurate; with hairs erect, or appressed; with 1 type of pubescence; puberulent; with pubescence golden; with pubescence uniformly distributed; with simple hairs; pliable; with hair bases plain; eglandular; without spines; not smooth; with elevated features; veined; longitudinally veined relative to fruit length; not tuberculate; longitudinally and irregularly wrinkled; exfoliating in part, or not exfoliating; without cracks; without embedded tissue, much thicker than epicarp, running from base to apex. Mesocarp present; thin; surface not veined; 1-layered; without balsamic vesicles; without fibers; without reniform canals; solid; (sub-) ligneous, or coriaceous. Endocarp present; visible; dull; opaque; monochrome; reddish brown, or tan; smooth; without adhering pieces of testa; nonseptate, or subseptate (because of intursion of fruit); with septa eglandular; chartaceous; not exfoliating; remaining fused to mesocarp and epicarp; without wings; entire. Seed(s) 1–8; length parallel with fruit length; neither overlapping nor touching; in 1 series. Funiculus 0.5–1.5 mm long; of 1 length only; thick; curved. Aril absent.

Seed: 4–5 mm long; 3.5–4 mm wide; 2.5–2.8 mm thick; not overgrown; not angular, or angular (somewhat); asymmetrical; oblong, or reniform, or triangular (more or less), or mitaform; compressed; with surface smooth; with visible radicle and cotyledon lobes; without external groove between radicle and cotyledon lobes; without hilar sinus; without umbo on seed faces; without medial ridge on each face. Cuticle not exfoliating; not inflated; not wrinkled. Testa present; without pieces of adhering epicarp; not adhering to endocarp; free from endocarp; dull, or glossy (somewhat); not modified by a bloom; colored; monochrome; dark to bright reddish brown, or orange; glabrous; smooth; coriaceous. Pleurogram absent. Pseudopleurogram absent. Fracture lines absent. Rim absent. Wing(s) absent. Raphe not visible. Hilum present; visible; with faboid split; with the lips of the faboid split the same color as the rest of the hilum; larger than punctiform; 0.3–0.5 mm long; with curved outline; circular; between cotyledon and radicle lobe; recessed; within rim; rim color of testa. Lens discernible; 0.5–1 mm long; with margins straight, or curved; wedge-shaped; elliptic; not in groove of raphe; adjacent to hilum, or confluent with hilum; 0.2 mm from hilum; barely mounded; similar color as testa; reddish brown; not within corona, halo, or rim. Endosperm present; thin; not pluglike and not resembling tip of radicle; covering entire embryo; adnate to testa. Cotyledons smooth; both outer faces convex; both the same thickness; both more or less of equal length; with both folded (barely), or not folded; not sufficiently folded for inner face to touch itself; portions of inner folded face unequal; margin entire 180 degrees from base of radicle; similar at apex; not concealing radicle; split over radicle; with lobes; with the interface division terminating at base of radicle; without margins recessed; red; inner face flat; glabrous on inner face. Embryonic axis deflexed; oblique to length of seed; without a joint evident between the radicle and the cotyledons. Radicle differentiated from cotyledon; bulbose; lobe tip straight; deflexed and parallel to cotyledon length; centered between cotyledons; less than 1/2 length of cotyledons. Plumule rudimentary; glabrous.

Distribution

Southern Europe.

Old World; southern Europe and Mediterranean.

Generic Notes

A note about children, An average of 3,000 per summer, being poisoned by fruits, seeds, and flowers of Laburnum in England was authored by Forrester (1979).

Tribal Notes

Tribe Genisteae

Traditionally this tribe has been called Genisteae. Reveal (1997) reported that the name Cytiseae was published before the name Genisteae. Following the International Code of Botanical Nomenclature (Greuter et al., 1994), the oldest name for a taxon must be used, so Reveal suggested that this tribe should be called Cytiseae. In 1999 Reveal (1999) reversed himself, so that this tribe remains the Genisteae. Bisby (1981) summarized tribe Genisteae, following the excellent study by Polhill (1976). Bisby correctly noted that "many species have been moved from one genus to another several times and the Cytisus-Genista complex has gained a reputation as a critical group." He continued with an indepth analysis of the tribe. Polhill (1994a, 1994b) and Van Wyk and Schutte (1995a), using chemical and morphological characters, transferred five genera from Crotalarieae (27) to Genisteae: Anarthrophyllum (30.06), Argyrolobium (30.03), Dichilus (30.02), Melolobium, and Sellocharis (30.07). Cristofolini (1997) carried out a cladistic study of the tribe's biogeography, and discussed its early evolutionary history. López et al. (2000) studied the species of this tribe occurring in southwestern Spain and presented detailed descriptions for and a key to them.