Chapter 9: Crop Plants and Exotic Plants

CROTALARIA
Crotalaria spp., family Leguminosae
The genus Crotalaria contains some 325 species, recognizable by their papilionaceous flowers, smooth leaves, erect growth, roundish pods, and yellow, brownish-yellow, blue, or purple flowers (Bailey 1949*). McKee and Enlow (1931) stated that C. mucronata Desv. [C. striata DC.] was the only one of commercial importance in the United States. Ritchey et al. (1941) tested 11 species for forage, and McKee et al. (1946) stated that four species (C. intermedia Kotschy, C. lanceolata E. Mey., C. mucronata, and C. spectabilis Roth) were extensively grown, primarily in the South (fig. 102). Wheeler and Hill (1957*) listed only two species - C. mucronata and C. spectabilis. Their justification for the growing of crotalaria was that it -

Makes excellent growth on light sandy soil, where it is sown for cover and green manure crops.

Does not harbor nematodes or rootknot.

Is well nodulated with nitrogen-fixing bacteria.

Is an annual (except in nonfreezing areas).

Sets seed in abundance.

The drawbacks to the cultivation of crotalaria are that it -

Contains an alkaloid that is poisonous to livestock or poultry (particularly the showy C. spectabilis).

Has a tendency to harbor certain insects harmful to citrus and pecans.

Has hard seeds that tend to germinate and come up years later and contaminate other crops.

Is treated as a noxious weed in at least one State if the seeds are harvested with corn or soybeans.

Because of these drawbacks and their significance at present, the crop is not being planted and the seed is almost unavailable.

Inflorescence:
Free (1970*), referring to work by Howard et al. (1919), stated that the large showy flowers of C. juncea L. occur in inflorescences, each flower having 10 stamens, five with short filaments and long narrow anthers, and five with long filaments and small round anthers. The long anthers dehisce in the bud, then the filaments of the round anthers elongate and push the pollen to the orifice of the keel. When a heavy insect alights on the wings, the pressure forces the style forward, and a ribbon of pollen is pushed out the orifice and onto the insect's abdomen. When the pressure is released, the style retracts through the mass of pollen, and another ribbon of pollen is extruded on the next insect's visit.

Roberts (1939) stated that crotalaria was a source of some nectar and an abundance of pollen. He did not explain how the bee collects the nectar. Pellett (1947*) stated that a colony of honey bees near Winter Haven, Fla., stored 50 pounds of dark and poor quality honey from C. mucronata and that the bees worked C. spectabilis to some extent. The effects of these visits on the flowers was not mentioned.

Pollination Requirements:
The pollination requirements of crotalaria are not too well understood. Todd (1957*) listed crotalaria as largely self-pollinated. Free (1970*) in discussing C. juncea stated that "When flowers are not visited by insects the continual elongation of the filaments presses the pollen masses onto the stigma so that self-pollination is possible. However, self-fertilization does not occur unless the stigmatic surface is rubbed against an insect's body, and lack of pollinators probably helps to explain why in parts of India few flowers set seed." A study of the effect of pollinating insects on the volume of seed produced by the different species of crotalaria and also on the germination of the seed would be of interest.

Pollinators:
Honey bees seem to be suitable pollinators.

Pollination Recommendations and Practices:
None.

LITERATURE CITED:
HOWARD A., HOWARD, G. L. C., and RAHMAN, K. A.
1919. STUDIES IN THE POLLINATION OF INDIAN CROPS. lndia Dept. Agr. Mem., Bot. Ser., 10: 195 - 220.

MCKEE, R., and ENLOW, C. R.
1931. CROTALARIA, A NEW LEGUME FOR THE SOUTH. U.S. Dept. Agr. Cir. 137, 30 pp.

MCKEE, R., STEPHENS, J. L., and JOHNSON, H. W.
1946. CROTALARIA CULTURE AND UTILIZATION. U.S. Dept. Agr. Farmers' Bul. 1980, 17 pp.

RITCHEY, G. E., MCKEE, R., BECKER, R. B., and others.
1941. CROTALARIA FOR FORAGE. Fla. Agr. Expt. Sta. Bul. 361, 72 pp.

ROBERTS, A. C.
1939. CROTALARIA. Amer. Bee Jour. 79: 84.