Fecundity above the species level: ovule number and brood size in the genisteae (fabaceae: papilionoideae)

Abstract

Per-fruit components of fecundity (ovules per ovary, seeds per fruit, seed: ovule ratio, and patterns of seed maturation within pods) were studied in 33 species of the Genisteae, a legume tribe of mostly Mediterranean shrubs, e.g., Cytisus, Ulex, that also includes more widespread herbs such as Lupinus. Species identity explained most variance in both potential (ovules) and realized (seeds per fruit and seed: ovule ratio) fecundity, and although significant population-specific effects existed, these were relatively small, indicating that estimates of fecundity were not particularly prone to environment-induced changes. Average seed: ovule ratios varied between 20% (for a few species in which fixed rates of embryo abortion result into single seeded pods) and 100% (annuals), but most taxa were in the 40%-60% range. The probability that an ovule near the base of the ovary matured into a seed was significantly lower than the pod average in the majority of species. As indicated by the large size of stigmatic pollen loads, this was unlikely to result from insufficient pollination but rather from preferential embryo abortion. High abortion rates next to pod base occurred in both presumed selfers and obligate outcrossers. Evidence points to relatively stereotyped reproductive ways and high reproductive coherence in the tribe, with major departures from the norm being high seed: ovule ratios exhibited by annual Lupinus (associated with selfing), and low ratios shown by species with single seeded pods (associated with fixed rates of embryo abortion).