FLOWERING PHENOLOGY, POLLEN FLOW, AND SEED PRODUCTION IN MARATHRUM-RUBRUM (PODOSTEMACEAE)

Podostemaceae (river weeds) are restricted to river-rapids and waterfa lls, Reproductive systems in the family are poorly understood. Studies of floral phenology and seed production in manipulated flowers were c onducted on Marathrum rubrum Novelo and Philbrick. Plants of M. rubrum are annual, flower profusely and set abundant seed. The duration of f lowering was 3-4 days. The bisexual flowers exhibit protogynous develo pment: stigma receptivity prior to anther dehiscence, All control flow ers developed fruits with seeds. Emasculated and bagged flowers did no t produce seeds. Experimental evidence indicates that M. rubrum is sel f-compatible. Similar levels of seed-set in control and bagged flowers suggest that autogamy is an important component of the breeding syste m. Mean seed-set in emasculated unbagged flowers (test for outcrossing ) was 101 for 1992 and 35 for 1995. Mean outcrossed seed-set (relative to the mean number of ovules per fruit) was 10.7% (1992) and 3.7% (19 95). These results illustrate that M. rubrum is not exclusively autoga mous. Additional study of the genetic consequence of this outcrossing is needed. (C) 1998 Elsevier Science B.V. All rights reserved.