Chapter 3: Clover and Some Relatives

SUBTERRANEAN CLOVER⁴²Trifolium subterraneum L., family Leguminosae
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⁴² See "Clovers, General."

Plant:
Subterranean clover is a low, pliant, running, reseeding, annual legume, with short seedstalks that carry clusters of three to four small creamy to pinkish flowers. It will grow on soil with fertility so low white clover will not thrive. As a winter annual in both Southern and Northern Hemispheres, subterranean clover blooms and sets seed in spring or early summer. The seed is dormant until fall, at which time it germinates. The plant name is derived from the fruiting characteristics. The seed head is made up of a cluster of forked hairs or bristles turned back around the seed pods. The ripening seed head turns downward, and the forked hairs help to bury many of the heads in the soil, somewhat like a peanut, but about half of the heads remain above ground (Lancaster 1949, Smith 1948).

Inflorescence:
The flower is made up of three to seven, usually four, perfect, papilionate, usually white, florets. The ovary of each floret contains two ovules, but usually only one develops (Morley 1961). Yates (1957) found that above-ground seeds were poorer in quality than those that developed below the ground surface. Howell (1960) stated that this clover can be distinguished from other annual species in Western United States by its non-involucrate head of fertile flowers that become abruptly deflexed on their very short pedicel after they open. At that time, numerous sterile flowers develop, enclosing the fertile ones in the burrlike cluster.

Pollination Requirements:
Todd (1957*) placed subterranean clover in the group of plants considered to be largely self-pollinated. A reference by Knuth (1908*, p. 297) that the flowers "are capable of self-fertilization, though perhaps they do not always do this," leaves some doubt that maximum seed production results from selfing. Morley (1961) considered the species self-fertilizing but with occasional hybridization by outcrossing. How insects can get to the flowers, which are likely to be covered by the plant's leaves, is not explained. More study on this plant should be made to determine if it is benefited by visitation from pollinating insects.

Pollinators:
Morley (1961 ) stated that he had observed honey bees working the flowers, but only after fertilization would have taken place. However, he did not exclude them entirely as a cause of hybridization.

Pollination Recommendations and Practices:
None.

LITERATURE CITED:
LANCASTER, R. R.
1960. SUBTERRANEAN CLOVER (TRIFOLIUM SUBTERRANEUM) IN CALIFORNIA AND OREGON. West. Bot. Leaflet (San Francisco) 9(7): 114-115.

LANCASTER, R. R.
1949. CLOVERS FOR TEXAS PASTURES. Tex. Agr. Ext. Serv. B-168, 24 pp.

MORLEY, F. H. W.
1961. SUBTERRANEAN CLOVER. Adv. in Agron. 13: 57-123.

SMITH, E. G.
1948. SUBTERRANEAN CLOVER IN CANTERBURY PASTURES. New Zeal. Jour. Agr.76: 293-294.

YATES, J. J.
1957. SEED SETTING IN SUBTERRANEAN CLOVER (TRIFOLIUM SUBTERRANEUM L.). I. THE IMPORTANCE OF THE MICRO-ENVIRONMENT. Austral. Jour, Agr. Res. 8(5): 433-443.