Crotalaria L.

Legumes of the World. Edited by G. Lewis, B. Schrire, B. MacKinder & M. Lock. Royal Botanic Gardens, Kew. (2005)

Habit

Shrubs, shrublets or perennial herbs, rarely small trees or annual herbs

Ecology

Seasonally dry tropical, subtropical to warm temperate forest, woodland, xerophytic shrubland and grassland, often in disturbed places, on sand or rocky outcrops

Distribution

especially in the southern hemisphere: most spp. in Africa and Madagascar (c. 510 spp., mostly E and southern Africa, c. 34 of which endemic to Madagascar and 5 widespread in Old World); c. 18 spp. widespread in tropical Asia; c. 60 spp. endemic to the Indian subcontinent; c. 5 spp. to W Asia, c. 15 spp. to Indo-China, c. 12 spp. to China, c. 6 spp. to Malesia and 9 spp. to Australia; 59 spp. endemic (and a further 15 introduced) in the New World (fide Windler & Skinner in ms.), with c. 35 spp. in S America (mainly Brazil), 20 spp. in N and C America (mainly Mexico) and c. 5 spp. widespread in New World

Note

Crotalaria appears to be closely related to Lotononis (q.v.); the two genera are unique in the family in their accumulation of several macrocyclic pyrrolizidine alkaloids (Van Wyk & Verdoorn, 1990); pyrrolizidine bases, however, are also known (Kinghorn & Smolenski, 1981: 592-593) from Ammodendron (Sophoreae) and Adenocarpus and Laburnum (Genisteae); infrageneric relationships are poorly known but the genus seems to have originated in Africa, with more recent diversification into other regions of the world; the Asian species are in need of revision

The current state of knowledge of the Crotalarieae was reviewed by Van Wyk (1991a) and by Van Wyk & Schutte (1995a). The most conspicuous recent change has been the exclusion of the Argyrolobium group (six genera, i.e. Argyrolobium, Dichilus, Melolobium, Polhillia, Anarthrophyllum and Sellocharis), which belong in tribe Genisteae rather than in Crotalarieae, where they were previously placed (Polhill, 1981q: 399 –402). New insights into relationships within the tribe have come mainly from chemosystematic studies of alkaloids (summarised in Van Wyk & Verdoorn, 1990) and several recent generic monographs (see below).

The Crotalarieae forms part of a monophyletic clade, the ‘core genistoids’ (Fig. 36) which also includes Genisteae, Podalyrieae, Thermopsideae, Brongniartieae, Euchresteae and Sophoreae sens. strict. (Crisp et al., 2000; Pennington et al., 2000a; Kajita et al., 2001). Crotalarieae appears to be sister to the Genisteae and both are sister to the Podalyrieae (Crisp et al., 2000; Wojciechowski et al., 2004). This clade is in turn sister to the Thermopsideae and Sophoreae sens. strict. (including Euchresteae).

The Crotalarieae shares with the Podalyrieae the absence of a-pyridone alkaloids such as cytisine and anagyrine that are a typical feature of all other ‘core genistoid’ tribes. Despite a lack of defining characters, the monophyly of the tribe as circumscribed here is well supported by molecular evidence (Crisp et al., 2000; Wink & Mohamed, 2003) and by cladistic analyses of morphological, cytological and chemical characters (Van Wyk & Schutte, 1995a). The latter study suggested an early diversification of the genera with uniform anthers and lupanine-type esters of quinolizidine alkaloids (Pearsonia, Rothia and Robynsiophyton) followed by the poorly known Spartidium and then the so-called ‘Cape group of genera’ (Polhill, 1981q: 399–402), which now includes Lotononis and Crotalaria. Relationships between the seven genera of the ‘Cape group’ remains unresolved despite several recent molecular studies because sampling is still relatively poor. However, a basally branching position in the tribe of the ‘Cape group’, notably Lebeckia and Wiborgia — as considered by Polhill (1976, 1981q) — is now accepted here. The exclusion of the Argyrolobium group, based on morphological and chemical characters, is also strongly supported by DNA sequence data. Due to reticulate and overlapping patterns of character state distribution in the Crotalarieae sens. strict., generic delimitations are intricate and subject to misinterpretation. Several of the large and diverse genera appear to be either monophyletic or paraphyletic depending on the choice of characters. As currently circumscribed the tribe includes 11 genera and c. 1204 species (Fig. 37).

M. Thulin et al. Flora of Somalia, Vol. 1-4 [updated 2008] https://plants.jstor.org/collection/FLOS

Morphology General Habit

Herbs or shrubs

Morphology Leaves

Leaves simple, 1-foliolate or digitately 3(–7)-foliolate

Morphology Reproductive morphology Inflorescences

Inflorescences usually terminal or leaf-opposed racemes

Morphology Reproductive morphology Flowers Calyx

Calyx-lobes (4–)5 or sometimes 3 by union of upper and lateral lobes

Morphology Reproductive morphology Flowers Corolla

Corolla usually yellow; keel rounded or angled, usually with a prominent beak

Morphology Reproductive morphology Flowers Androecium Stamens

Stamens all joined; 5 long and 5 short anthers

Morphology Reproductive morphology Fruits

Pod usually inflated, dehiscent, 1–many-seeded.

Distribution

Over 700 species, throughout the tropics and subtropics particularly of the southern hemisphere, but most numerous in tropical Africa, from where about 500 are recorded.

Leguminosae, J. B. Gillett, R. M. Polhill & B. Verdcourt. Flora of Tropical East Africa. 1971

Morphology General Habit

Herbs or shrubs of very varied habit

Morphology Leaves

Leaves simple, 1-foliolate or digitately 3(–7)-foliolate; leaflets entire

Morphology Leaves Stipules

Stipules filiform to foliaceous or absent

Morphology Reproductive morphology Flowers

Flowers usually in terminal, leaf-opposed or less commonly axillary racemes, sometimes modified as heads, subumbelliform or compound, occasionally flowers solitary or in axillary clusters

Morphology Reproductive morphology Flowers Calyx

Calyx (4–)5-lobed or sometimes effectively 3-lobed by union of upper and lateral lobes on either side; tube sometimes protracted on the lower side or 2-lipped

Morphology Reproductive morphology Flowers Corolla

Corolla usually longer than the calyx, usually yellow or yellow-green, variously marked, less commonly white or blue; standard almost always with 2 callus-like appendages at the base inside, glabrous or pubescent outside; wings with rows of crescent-shaped folds between some of the veins; keel rounded or angled, generally produced into a prominent beak

Morphology Reproductive morphology Flowers Androecium Stamens

Stamens all joined, with the sheath open at least at the base; anthers dimorphic, 5 large alternating with 5 small

Morphology Reproductive morphology Flowers Gynoecium Pistil

Ovary usually stipitate; style curved or geniculate, almost always pubescent above; stigma usually small, rarely bilobed

Morphology Reproductive morphology Fruits

Pods subsessile to long-stipitate, usually inflated, almost always dehiscent, though sometimes tardily so, 1–many-seeded

Morphology Reproductive morphology Seeds

Seeds mostly oblique-cordiform to oblong-reniform, sometimes with a conspicuous aril.

Leguminosae, various authors. Flora Zambesiaca 3:7. 2003

Morphology General Habit

Herbs or shrubs.

Morphology Leaves

Leaves simple, 1-foliolate or digitately 3(7)-foliolate, usually petiolate; stipules filiform to leaf-like or lacking.

Morphology Reproductive morphology Flowers

Flowers usually in terminal, leaf-opposed or less commonly axillary racemes, occasionally solitary or clustered; bract and paired bracteoles generally present.

Morphology Reproductive morphology Flowers Calyx

Calyx usually with 5 subequal lobes, sometimes the lower 3 on a short lip, sometimes 2-lipped with long lobes, occasionally with only 4 lobes or with the lateral and upper lobes largely joined on either side.

Morphology Reproductive morphology Flowers Corolla

Standard generally yellow, sometimes blue or white, often lined reddish, almost always with 2 appendages at the base inside, glabrous or hairy outside; keel rounded to angled, generally produced into a well developed beak.

Morphology Reproductive morphology Flowers Androecium Stamens

Stamens all joined into a sheath open at least at the base; anthers alternately long, basifixed, and smaller, dorsifixed.

Morphology Reproductive morphology Flowers Gynoecium Pistil

Style curved to geniculate, the basal portion thicker, almost always with 1–2 lines of hairs on the upper part; stigma small.

Morphology Reproductive morphology Fruits

Pod subsessile to long-stipitate, usually inflated, generally dehiscent, sometimes tardily so, 1–many-seeded.

Morphology Reproductive morphology Seeds

Seeds mostly oblique-cordiform to oblong-reniform, with a definite hilar sinus,sometimes with a conspicuous aril.

Use

Several species are of commercial importance as fibre crops, fodder and green manure; others are used as medicine, ornamentals, nurse crops, heavy metal indicators, human food and for soil improvement (intercropping); some cause crotalism in livestock and humans - acute but more often chronic poisoning affecting the lungs and liver - due to the ingestion of pyrrolizidine alkaloids with an unsaturated necine base; C. juncea L. (Sunn hemp) , is a major crop for its bark (phloem fibres) which provides a high quality bast fibre for cordage, fishing nets and fine paper

Use

Several species are recorded as having pods and/or seeds which are toxic for domestic animals. However, the foliage of some species is said to be good for browse.