Trifolium

Taxonomy

Trifolium C. Linnaeus Sp. Pl. 764. 1 Mai 1753.

Subfamily: Faboideae.
Phylogenetic Number: 3.21.06.
Tribe: Trifolieae.
Species Studied - Species in Genus: 121 studied; ca. 250 in genus.

Description

Fruit: A legumelegume:
usually dry, dehiscent fruit derived from a single carpel that opens along two longitudinal sutures
, or a nutletnutlet:
small, hard, indehiscent, one-seeded fruit
; unilocular; 0.14–1.5 cm long; 0.04–0.5 cm wide; length less than twice as long as width, or 2–9 times longer than wide; with deciduous androecial sheath; with persistent corolla, or deciduous corolla; with standard petal; with persistent calyx; with calyx longer than fruit, or shorter than fruit; without orifice formed by curving of fruit or fruit segments; straight; not plicate; not twisted; asymmetrical, or symmetrical; oblong (to linear or ovate), or ovate, or elliptic, or fusiform, or lanceolate, or linear, or dolabriform, or falcate; with both sutures parallelly curved; inflated, or not inflated; compressed; without beak; short tapered at apex, or rounded at apex; with the apex and base uniform in texture, or differing in texture; fragile, thinner than chartaceous, like Trifolium, or membranous, or chartaceous, or coriaceous, or leathery (rarely); seed chambers externally visible, or invisible; margin constricted, or not constricted; margin slightly constricted along both margins; margin without sulcus; margin plain; wing(s) absent; substipitate, or nonstipitate; indehiscent, or with all layers dehiscing (with 2 or 1 prominent sutures); splitting along suture(s). Dehiscence of valves along 1 suture, or both sutures; passive. Replum invisible. Epicarp dull; monochrome; brown (various shades, yellowish); with surface texture uniform; glabrous, or glabrate; with hairs erect; with 1 type of pubescence, or 2 types of pubescence; pilose, or puberulent (slightly); with pubescence gray; with apical pubescence different from basal pubescence; with apical 1/4 tomentose and basal 3/4 glabrous, or apical 3/4 tomentose and basal 1/4 glabrous; with simple hairs; pliable; with hair bases plain; eglandular; without spines; not smooth; with elevated features; veined, or not veined; longitudinally veined relative to fruit length (occasionally), or reticulately veined; not tuberculate; not exfoliating; without cracks; without embedded tissue, much thicker than epicarp, running from base to apex. Mesocarp absent. Endocarp present; visible; dull, or glossy; translucent, or opaque (rarely); monochrome; tan, or white; smooth; without adhering pieces of testa; nonseptate; chartaceous; not exfoliating; remaining fused to epicarp; without wings; entire. Seed(s) 1–10. Funiculus of 1 length only. Aril absent.

Seed: 0.8–5 mm long; 0.8–3 mm wide; not overgrown; not angular; symmetrical, or asymmetrical; circular, or mitaform, or oblong, or pyriform, or quadrangular, or reniform, or rhombic, or triangular; terete, or compressed, or flattened; with visible radicle and cotyledon lobes, or without visible radicle and cotyledon lobes; without external groove between radicle and cotyledon lobes; 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; glossy, or dull; not modified by a bloom; colored; monochrome, or mottled, or streaked; with frequent mottles; with frequent streaks; black (to reddish, greenish, purplish, yellowish, dark, or reddish), or green (yellowish to pale), or red, or tan, or yellow (to lemon); with black overlay, or brown overlay (various shades), or purple overlay; glabrous; smooth, or not smooth; with elevated features, or recessed features; shagreen, or tuberculate (minutely), or warty (finely), or wrinkled; pitted with small separate pits; 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; punctiform; between cotyledon and radicle lobe; not within corona, halo, or rim. Endosperm present; thin; not pluglike and not resembling tip of radicle; covering entire embryo. Cotyledons smooth; both outer faces convex; both the same thickness; both more or less of equal length; not folded; margin entire 180 degrees from base of radicle; similar at apex; not concealing radicle; entire over radicle; without lobes; with the interface division terminating at base of radicle; without margins recessed; 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, or linear; lobe tip straight; deflexed and parallel to cotyledon length; centered between cotyledons; 1/2 to nearly length of cotyledons, or equaling length of cotyledons. Plumule rudimentary; glabrous.

Distribution

Temperate and subtropical regions of the Northern and Southern Hemispheres.

New World, or Old World; pansubtropical, or pan warm temperate; Alaska, Canada, United States, Mexico, Central America, and South America; Argentina, Peru, Brazil, and the Guianas; Europe, Mediterranean, Russia, China, Japan, Africa, Madagascar, Southwest Asia, India, Korea, Macaronesia, and Mongolia.

Worldwide crop.

Generic Notes

Zohary and Heller (1984), in discussing the evolution of the legumelegume:
usually dry, dehiscent fruit derived from a single carpel that opens along two longitudinal sutures
(their legumen) in the genus Trifolium, noted that section Lotoidea had the most primitive legumelegume:
usually dry, dehiscent fruit derived from a single carpel that opens along two longitudinal sutures
in the genus. These legumes are often 2–9-seeded and dehiscent by both sutures. From this primitive state, the advanced one-seeded "utricle or nutletnutlet:
small, hard, indehiscent, one-seeded fruit
" evolved with a membranous pericarp that may consist of only an epidermal layer. These legumes do not dehisce but split transversely (circumscissly) or irregularly, and are found in section Trifolium and even in advanced species in section Lotoidea. Some fruits are operculate. Unlike other legumelegume:
usually dry, dehiscent fruit derived from a single carpel that opens along two longitudinal sutures
genera, the fruiting heads of a few species of Trifolium separate from the plants and serve as the unit of dispersal. In Trifolium subterraneum C. Linnaeus fertile flowers are pushed into the ground where the fruits and seeds mature. See Arachis (14.26) and Medicago (21.05).

Tribal Notes

Tribe Trifolieae

Endo and Ohashi (1997) have proposed, after a cladistic analysis using morphological characters, including internal seed morphology, that Cicereae (20) and Fabeae (19) formed a monophyetic group whose sister group is Trifolieae. Ononis and Parochetus (21.02) "are not nearly as closely related to the remaining four genera as the latter are to each other, and indeed that the two genera are not at all closely related to each other (or so far as I know to anything else)" (E. Small, pers. comm. 1997). Butler (1996) presented a table with eight seed characteristics of 14 Medicago (21.05) spp., seven Melilotus (21.03) spp., 25 Trifolium (21.06) spp., 11 Trigonella (21.04) spp., and two Ononis spp. as an aid for their identification in archaeological sites.