We studied the flower duration, the phenology of flowering and fruiting, and flower, fruit, and seed production in three Genisteae shrub species of the W Mediterranean Region: Cytisus multiflorus, C. striatus, and Retama sphaerocarpa. Flower duration was negatively correlated with temperature, and in the case of C. striatus it was also influenced by pollination. In Cytisus multiflorus, which flowers during winter in the population studied, two floral morphs were recognized differentiated by flower size, phenological pattern, and production of the reproductive organs: morph LF (large flowers) and morph SF (small flowers). The former is earlier in phenology but its reproductive success is less than the second since it not only produces significantly fewer flowers/plant, but also a smaller crop of fruit and seeds. The flowering of the LF morph lasted some three months and of the SF morph 11 weeks. The winter-spring flowering C. striatus, with a four month duration of flowering time, is sympatric with C. multiflorus and their flowering periods overlap, but the former is more successful reproductively. Retama sphaerocarpa is clearly spring flowering, with an extremely short duration of flowering (c. 6.5 weeks), but, unlike the other two species which disperse their seeds in the same season in which they are produced, it staggers the dispersal of its diaspores over more than one year. Despite the great flower per plant production, especially in Retama sphaerocarpa, and of the number of fruit initiated, the final crop of fruit and seed/plant is low in the three species (C. multiflorus: fruit 8.40% and seeds 1.96%; C. striatus: fruit 13.09% and seeds 4.12%; Retama sphaerocarpa: fruit 5.65% and seeds 1.33%).
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"C. multiflorus is an endemic shrub of the western Iberian Peninsula, with winter–spring flowering, having a large number of white flowers per plant, a valvular type of pollen presentation and very low fruit set percentage after natural pollination (Ló pez et al. 1999; Rodríguez-Riañ o et al. 1999a, 2004). C. striatus is an endemic shrub of the western Iberian Peninsula and north-west Morocco, with spring flowering, having a large number of yellow flowers, an explosive type of pollen presentation and also a very low fruit set percentage after natural pollination (Ló pez et al. 1999; Rodríguez-Riañ o et al. 1999a,b). Both species present a monosporic Polygonum-type of embryo sac development, a typical embryo development (proembryo, globular, heart, torpedo, and cotyledon phases), a nuclear endosperm development and seeds presenting a characteristic aril of funicular origin (Rodríguez-Riañ o et al. 2006). "
[Show abstract][Hide abstract] ABSTRACT: Seed formation involves not only the embryo and endosperm development, but also the formation of a series of either ephemeral or non-ephemeral structures. In this article, we study several of those structures in Cytisus multiflorus and Cytisus striatus. The endosperm development is first nuclear and later cellular, except for the chalazal area, whose development is always nuclear. It generates, in the early developmental stages, a sac-like haustorium. As the seed develops, two structures seem to be closely related to nutrient mobilization to the embryo sac: on the one hand, a group of cells and a channel, located
in the chalazal area and closely related between them and to the endosperm haustorium, which could be interpreted as a hypostase and on the other hand, an endothelium, derived from the inner integument, which later degenerates leaving no trace in the mature seed. All of these structures would be associated with the directionality of assimilates from ovule tissues to embryo sac. In mature seed and surrounding the embryo appears a unicellular layer of cells rich in proteins (aleurone layer), which is the origin of the outermost layer of the cellular endosperm. The seed coat is made up only of the outer integument.
"(Rodríguez-Riaño, Ortega-Olivencia & Devesa, 1999b). There is no doubt, therefore, that flower longevity is related to the season in which flowering takes place, increasing with cooler temperatures and wetter environments (Primack, 1985; Rodríguez-Riaño et al., 1999b; also see Rathcke, 2003). In some species, the long lifespan of the flowers has been interpreted as a mechanism to avoid competition and to ensure reproduction (for example, "
[Show abstract][Hide abstract] ABSTRACT: We studied the reproductive biology of two leguminous shrubs endemic of the western Meditenanean region Cytisus striatus (Hill) Rothm. and Retama sphaerocarpa (L.) Boiss. The former is polliniferous, and the l atter is nectariferous, with maximum nectar production at the earliest hours of the morning. Germination of the pollen grains
in the flowers of the two species occurs only after rupture of the stigmatic surface. It is also necessary in both cases that pollinators (mainly Apis mellifera) visir the flowers for fruit and seed set to occur. Our study of the pollen-pistil interaction indicated that there exists prezygotic self-incompatibility in these two species, probably of the gametophytic type, but some self-pollen tubes escape this control and self-fertilize some ovules. However, after hand sel f-pollination, fruit and seed set is very low for both species. This suggests the existence of a postzygotic rejection mechanism, which could be due either to the existence of late-acting self -incompatibility or to an early action of inbreeding depression, although there are lines of evidence that seem to point to the second possibility. Hand cross-polli nation led to an increased number of fruit and seeds per plant relative to the control plants, indicating that reproduction is pollen limited.
Canadian Journal of Botany 10/1999; 77(6):809-820. DOI:10.1139/cjb-77-6-809 · 1.40 Impact Factor