Inhaltszusammenfassung

The reproductive biology of the mycoheterotrophic Voyria caerulea, V. clavata and V. rosea (Gentianaceae) was studied in French Guiana. Floral characteristics indicated adaptations to long-tongued flower visitors. The three species possess large, conspicuously colored flowers that produced sucrose-rich nectar (concentrations: 16.4%-23.9%) and emit a rosy floral perfume with a citrus-related aspect, dominated by terpenoids. Principal scent compounds of V. caerulea and V. rosea were (E)-nerolid...The reproductive biology of the mycoheterotrophic Voyria caerulea, V. clavata and V. rosea (Gentianaceae) was studied in French Guiana. Floral characteristics indicated adaptations to long-tongued flower visitors. The three species possess large, conspicuously colored flowers that produced sucrose-rich nectar (concentrations: 16.4%-23.9%) and emit a rosy floral perfume with a citrus-related aspect, dominated by terpenoids. Principal scent compounds of V. caerulea and V. rosea were (E)-nerolidol and geraniol, and (E)-8-oxo-β-farnesene [(E)-2,6-dimethyl-10-methylenedodeca-2,6,11-trien-5-one, a new natural product] and (E,E)-farnesyl acetate in V. clavata. Germinating pollen grains were observed in the anthers of all species, forming large interwoven clumps that were transferred by the pollinators as a unit. In V. caerulea and V. rosea, stamens and stigmas were positioned close together, enabling the plants to self-pollinate. In contrast, male and female organs are widely separated in V. clavata. Pollen to ovule ratios of all species were low (33-78), indicating that pollen transfer (either by selfing or by outcrossing) is very efficient. Flower visitors were butterflies (V. caerulea, V. rosea) and/or long-tongued bees of the genus Euglossa (V. clavata, V. rosea). Nevertheless, Voyria caerulea and V. rosea were visited only rarely and irregularly. We suggest that these two species follow a mixed selfing-outcrossing strategy to ensure seed production when pollen transfer by visitors fails. In contrast, V. clavata showed a high degree of specialization towards euglossine-pollinators, which were frequent visitors. The close plant-pollinator interaction increases the probability of outcrossings and might have enabled this species to completely rely on pollinators for reproduction. Average seed set in the studied species ranged between 36% and 49% and was very variable among individuals, probably due to resource-limitation. The capsules of V. caerulea and V. clavata showed characteristics of endozoochorous dispersal and were frequently found damaged by possible rodent dispersal agents.» weiterlesen» einklappen

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