Reproductive Characteristics And Fruit Polymorphyism In Two Ephemeral Species Of Lappula

Lappula duplicicarpa and L. semiglabra(Boraginaceae)are early-spring ephemerals common in the Junggar Desert. They produce heteromorphic fruits, and nutlets developed from each flower differ in their morphology, pattern of detachment and method and distance of dispersal. Germination characteristics, phenological characteristics, breeding system, reproductive allocation, fruit-set and seed-set pattern and fruit dispersal strategy of them were studied, and life-history and reproductive strategies of both species and their adaptation to desert environment were discussed. The main results are as follows:1)Phenological characteristics: Sibling nutlets of both species could germinate in both spring and autumn. In spring, nutlets germinate at the end of March and fruits matured in the middle of May, and the life cycles were about 75d and 78d, respectively.2)Breeding system:①Flowers of both species are bisexual. Neither flower morphology, pollen number, ovule number or P/O ratio of individual flower or of the"population"of flowers in the inflorescence had a direct relationship to production of heteromorphic nutlets.②Anthesis of individual flower in both species lasted about 24 h and was not affected by weather conditions.③Fertility rates of pollen were 91.0±4.7% in L. duplicicarpa and 93.2±4.3% in L. semiglabra.④In both species, pollen viability was low at the beginning of anther dehiscence (71% in L. duplicicarpa and 65% in L. semiglabra), and survivorship (viability) curves for pollen were similar. The optimal pollination period was 0-2 h and 0-3 h after anthesis in L. duplicicarpa and L. semiglabra, respectively, and the optimal stigma receptivity for both species was 0-3 h after anthesis. Thus, the optimal pollination period was highly correlated with the period of high stigma receptivity.⑤P/O ratios of L. duplicicarpa and L. semiglabra were 1222±197 and 3419±426, respectively. The breeding system of both species is facultative mixed, which is consistent with the results of bagging experiments without emasculation and with observation on pollen tube growth in stigmas of selfed flowers using fluorescence microscopy.3) Reproductive allocation, fruit-set and seed-set pattern: The plants of both species favored to allocate a great proportion of resources to reproductive activities, and the reproductive allocation were 53.45% and 50.67%, respectively. The reproductive output of plants was size-dependent, the reproductive output increased with plant size, and fruit set increased with plant biomass. Fruit-set rate were 97.56% and 97.94%, respectively and seed-set rate were 91.35% and 86.94%, respectively. A large proportion of the flowers were those that produced 4 nutlets in both species.4) Morphology of fruit and dispersal strategy: The combinations of four nutlets with short and long glochids varied at the different position of the infructescence. There are very significant differences between dimorphic nutlets in weight, length of glochids, morphological and micromorphological characteristics of nutlet. The pericarp of nutlets with long glochids are thicker than that of those with short glochids, and there appears abscission layer between nutlet with long glochids and gynophore at the end of development. Nutlets with long glochids are more easily detached by wind or by animals from the mother plants than those with short glochids, and they have a long dispersal distance. Nutlets with short glochids firmly attached to the gynobases are hard to detach from mother plants.