Flowering Behavior and Seed Development in Four Desmodium Species 1

A knowledge of flowering behavior and seed production would be helpful in formulating intra‐ and interspecific breeding programs of Desmodium species. Selections of D. canum (Gmel.) Schin. and Thell., D. intortum (Mill.) Urb., D. sandwicense E. Mey., and D. uncinatum (Jacq.) DC. were grown in controlled environments and in the glasshouse at Ithaca, New York to investigate plant response to photoperiod and to study ovule and seed development. D. sandwicense was day‐neutral. D. intortum and D. uncinatum flowered under short days of less than 12 hours. D. canum needed at least 12 hours to induce flowering under artificial light of 21,520 lux (2,000 ft‐c). The species is considered day‐neutral, however, since profuse flowering occurred under natural light of 15.2 hours and since it flowers under shorter days in tropical and subtropical areas. The four species had perfect flowers borne on indeterminate racemes. Anthers of D. canum dehisced in midafternoon with 14 to 15.2 hours of light in the glasshouse. Under 11 hours of light the other three species dehisced 6 to 8 hours before the end of the dark period in the growth chamber. A tripped flower wilted quickly and the standard petal folded over the stigma within 1 hour. Without pollinators, flowers generally did not trip, but seed set exceeded 50%. After fertilization, the ovule length:width ratio increased rapidly for 4 to 6 days, then declined as broadening occurred. The epicotyl, hypocotyl, and cotyledons became visible within 5 days. At 17 days after pollination seed coats became impermeable on drying of seeds. Before the seed reached maximum weight at about 28 days, 90% or more had hard seed coats. Seed were viable 20 days after fertilization when scarified, and germination rapidly increased thereafter to about 30 days. There was no dormancy period when seed were properly scarified.