Reproductive Patterns of two Varieties of Yucca whipplei (Liliaceae) with Different Life Histories

Abstract

Flower, fruit, and seed production were compared for two varieties of Yucca whipplei, Y. whipplei whipplei (which reproduces semelparously) and Y. whipplei caespitosa (which is iteroparous), to determine differences in fecundity with respect to leaf surface area. Vegetative characteristics such as leaf surface area and leaf area index, which are related to the potential for gas exchange and photosynthate production in these plants, and reproductive characteristics such as inflorescence size, total flowers, mature fruit, and seed production as well as seed viability were determined for individuals of each variety. There was no significant difference in leaf surface area between varieties, but the number of viable seeds produced per unit leaf surface area was greater for Y w. whipplei than for Y. w. caespitosa. There was a significant difference in seed quality between varieties; Y. w. whipplei had seeds that were 1.5 times more viable and germinated twice as fast as Y. w. caespitosa. The total number of viable seeds per plant increased with leaf surface area for Y. w. whipplei, but for Y. w. caespitosa the total number of viable seeds per plant increased with increasing rosette number per individual. For Y. w. whipplei, the percentage of viable seeds per plant decreased as inflorescence size increased. However, the total number of viable seeds produced was positively correlated with inflorescence size, indicating that for a greater investment in flowers and ultimately fruit, the plant received diminishing returns in terms of seed number. There was no such relationship for Y. w. caespitosa, indicating that attached rosettes may provide resources for producing viable seeds. These reproductive patterns are consistent with observed patterns of resource use in semelparous and iteroparous plants but allow new insight on size/fecundity patterns in closely related plants.