Chapter 3: Clover and Some Relatives

STRAWBERRY CLOVER⁴¹Trifolium fragiferum L., family Leguminosae
Strawberry clover is grown to a limited degree as a pasture plant in moist and alkaline soils in the west coast States and the northern Great Plains (Graham 1941 *, Davies 1 962).
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⁴¹ See "Clovers, General."

Plant:
Strawberry clover is a perennial low-growing plant with creeping stems that root at the node to spread vegetatively as well as by seeds. The plant is difficult to distinguish from white clover when not in bloom. In maturity, the seeds are pressed closely to the ground making harvesting difficult. Tiver (1954) stated that strawberry clover in South Australia is a prolific seed producer, which yields up to 250 pounds of seed per acre.

Inflorescence:
The flower heads are round, pink to white, and resemble a strawberry, hence the name of the plant. The blooms appear earlier than those of white clover. There may be 35 to 60 florets per head. Only one seed forms in a floret. As the seeds mature, the head takes on the appearance of a balloon. The flowers are extremely attractive to bees for both nectar and pollen.

Pollination Requirements:
Johnson (1951) and Williams (1931) considered strawberry clover self-fertile. Hollowell (1939) also stated that the flowers are self- fertile, that crossing between flowers is not necessary, but that honey bees assist in the transfer of pollen to the stigmas. Davis and Young (1966) stated that most specimens from the Mediterranean area were completely self-sterile, but as the plant spread northward it was conditioned by its environment, probably lack of pollinating insects, to evolve into a self-fertile plant. Morley (1963) stated that the flowers are not self-pollinating and are largely self-incompatible. He stated, "It is difficult to understand how strawberry clover has been regarded as self- pollinating for so long. Seeds are expensive but shouldn't be if adequate honey bees are provided." He harvested only 0.25 seed per flower where bees were infrequent, but 0.70 per flower where bees were plentiful. Tiver (1954) considered honey bees important in increasing seed yields. Hollowell (1960) also noted that seed yields were increased if honey bee colonies were adjacent to the field. Todd (1957*) listed strawberry clover in the group of plants "Seed production increased by Bees."

Peterson et al. (1962) stated that common strawberry clover is self-fertile, but bees help to move the pollen to the stigma. 'Saline' strawberry clover, however, is self-sterile and will not set seed without cross-pollination. In this case, bee activity is essential for seed production.

Wright (1964) made a study of the pollination requirements of strawberry clover using material from Australia and New Zealand. He studied 66 clones and learned that most of them were self-incompatible but that some set a relatively high percentage of seed autogamously; however, they set more seed if they were cross-pollinated. He also found that self-pollinated plants were less vigorous. He considered strawberry clover a cross-pollinated species and found a high correlation between set of seeds from hand and bee pollination.

Pollinators:
Honey bees seem to be the primary pollinators.

Pollination Recommendations and Practices:
Morley (1963) spoke of providing adequate honey bees for high seed yields. Hollowell (1939) stated that placing colonies of honey bees adjacent to flowering fields is necessary, but he did not indicate the number of hives per acre needed.

LITERATURE CITED:
DAVIES, D. J. G.
1962. PALESTINE STRAWBERRY CLOVER A USEFUL SPECIES FOR LOW- LYING SOILS. New Zeal. Jour. Agr. 104(1): 79, 81-82.

DAVIS, W. E., and YOUNG, N. R.
1966. SELF-FERTILITY IN TRIFOLIUM FRAGIFERUM. Heredity 21: 615-624.

HOLLOWELL, E. A.
1939. STRAWBERRY CLOVER. U.S. Dept. Agr. Leaflet 176, 8 pp.

______ 1960. STRAWBERRY CLOVER: A LEGUME FOR THE WEST. U.S. Dept. Agr. Leaflet 464, 8 pp.

JOHNSON, I. J.
1951. (TABLE 9.1.) In Hughes, H. D., Heath, M. E., and Metcalf, D. S., Forages, 724 pp. Iowa State College Press, Ames.

MORLEY, F. H. W.
1963. THE MODE OF POLLINATION IN STRAWBERRY CLOVER (TRIFOLIUM FRAGIFERUM L.). Austral. Jour. Expt. Agr. and Anim. Husb. 3(8): 5-8.

PETERSON, M. L., STREET, J. E., and OSTERLI, V. P.
1962. SALINA STRAWBERRY CLOVER. Calif. Agr. Expt. Sta. and Agr. Ext. Serv. Leaflet 146.

TIVER, N. S.
1954. STRAWBERRY CLOVER. So. Austral. Jour. Agr. 57: 317-325.

WILLIAMS, R. D.
1931. FERTILITY OF VARIOUS HERBAGE LEGUMES. SELF-AND CROSS- FERTILITY AND FLOWERING HABITS OF CERTAIN HERBAGE GRASSES AND LEGUMES. Welsh Plant Breed. Sta., Univ. Col. of Wales Aberystwyth, ser. H., No. 12: 221-227.

WRIGHT, D. S. C.
1964. SELF- AND CROSS-FERTILITY IN STRAWBERRY CLOVER (TRIFOLIUM FRAGIFERUM L.). New Zeal. Jour. Agr. Res. 7(1): 32-36.