The flower biology of Daphne gnidium L. (Thymelaeaceae)

Abstract

Daphne gnidium is a circum-Mediterranean\ud evergreen shrub. Flower and pollen features related to\ud pollination mechanism were analyzed, and the seasonal\ud presence of insects visiting the plant was monitored. The\ud morphology and functionality of flowers are compatible\ud with entomophily, as are pollen viability, which is maintained\ud for a few hours only after anthesis, and the very short\ud stigmatic receptivity. The reproductive fitness of the species\ud is low and the ripening process often fails (35% collapsed\ud embryos). While male organ functionality is fairly regular,\ud the female organ often shows developmental arrest. The\ud complex or transient evolutionary traits displayed by\ud D. gnidium are comparable to those of Thymelaea hirsuta\ud and other members of the Thymelaeaceae

Influence of reproductive traits on pollination success in two Daphne species (Thymelaeaceae)

“…Nevertheless, we found in either species no relationship between fruit set and pollen-grain germinability, as presumably very low fractions of outcrossing pollen grains appear to reach their stigmas. In both species, stigmas are completely covered by self-pollen after anthesis and, thus, it is likely that although fertilization may eventually occur, some selfincompatible mechanisms prevent fruit set when outcrossing pollen does not arrive to flowers, as has been suggested to occur in D. gnidium (Roccotiello et al 2009). There were no differences between self-induced and selfspontaneous hand-pollinations in other Daphne species (present work; Alonso and Herrera 2001), which suggests that spontaneous selfing treatment could be a proxy to detect self-incompatibility in hermaphrodite Daphne species.…”

“…Therefore, it is possible that a low fruit set is a characteristic of the genus Daphne, although not of other genera in the family, as for instance Thymelaea velutina ([50% fruit set; De la Bandera and Traveset 2006). In a recent study, Roccotiello et al (2009) point out that the low fruit set (5-18%) in D. gnidium seems to result from an embryo collapse during fruit development (i.e. 75% of immature fruits die out), which is likely derived from an apomictic process of self-pollination.…”

“…On the other hand, D. gnidium seems to be more resource limited than D. rodriguezii, as the former produced 40% less fruits in hand-cross pollinations than the latter. D. gnidium pistils can wither at early stages of flower development, which explains the reduction of the functionality of female organs (Roccotiello et al 2009). D. gnidium blooms during a period (from late summer to early autumn) when pollination service is much more reliable to allow outcrossing pollinations.…”

“…Flowers, whose position is terminal from inflorescences located in the apical part of new branches (Roccotiello et al 2009), open less synchronously than D. rodriguezii (i.e. the number of receptive flowers per plant of D. gnidium at flowering peak is less than 10%, compared with more than 50% in D. rodriguezii; pers.…”

“…For the non-emasculation treatment (intact anthers), we chose flowers the anthers of which had already dehisced (i.e. 2-3 day-old flowers), and thus, stigmas bore large amounts of self-pollen (Roccotiello et al 2009). Furthermore, we opened laterally all treated flowers in order to control for the possible effect of flower manipulation on fruit set.…”