Reproductive biology of a mycoheterotrophic species, Burmannia wallichii (Burmanniaceae)

Abstract

Received Jub 1999; acceptcdfor publtkation ~t c m b e r I999The breeding system of a mycoheterotrophic species, Bumannia wullkhii (Miers) Hook. f.(Burmanniaceae), is assessed using field observations, floral anatomy, pollen histochemistry and isozyme electrophoresis. The structure of the flower effectively prevents pollinators from accessing the stamens, and no pollinators were observed visiting natural populations in Hong Kong. The pollen is starch-rich but lipid-poor. Analysis of isozyme variation revealed a small proportion of polymorphic loci, a low level of total heterozygosity (HT=0.1972), and a very high overall hation index of populations (&=0.6602). These results strongly suggest that B. walluhii is predominantly self-pollinated. The coefficient of gene differentiation (GsT) is low (0.05), although it is suggested that this is due to genetic homogenization of populations consonant with the formation of numerous tiny 'diaspora' seeds that are wind dispersed.

Evidence for mixed sexual and asexual reproduction in the rare European mycoheterotrophic orchidEpipogium aphyllum, Orchidaceae (ghost orchid)

“…In his experiments, Geitler (1956) noted a similar percentage of seed capsules on flowering shoots that were manually self-pollinated or cross-pollinated. Some studies have suggested that autonomous self-pollination may be favourable for mycoheterotrophic plants, as they have limited access to carbon sources (Takahashi et al, 1993;Zhang and Saunders, 2000;Lehnebach et al, 2005) and are restricted to shaded forest understorey habitats with a paucity of pollinators (Dressler, 1993;Leake, 1994). However, the variety in flower morphology of many mycoheterotrophic plants instead suggests the diversity of breeding systems and pollinators, as has been confirmed by studies into the reproductive biology of Voyria (Hentrich et al, 2010) and Monotropoideae (Klooster and Culley, 2009).…”

Chasmogamy and entomophily in Burmannia disticha (Burmanniaceae)

“…The entire genus Burmannia is likely to possess a prominent entomophilous floral syndrome, as defined by Faegri and van der Pijl (1979) . This idea has already been proposed for various species of the genus ( Spitmann, 1975 ; Maas et al., 1986 ; Zhang and Saunders, 2000 ). Flowers of Burmannia are brightly coloured; in B. disticha , yellow tepal lobes contrast with the violet floral tube and ovary.…”

“…At the same time, the majority of species likely benefit from pollen-derived nutrients when consuming pollen-contaminated nectar ( Baker and Baker, 1975 ; Romeis et al., 2005 ). Pollen of Burmannia (including B. disticha ) was indicated as starch-rich but lipid-poor ( Zhang, 1999 ; Zhang and Saunders, 2000 ), which is typical of plants pollinated by Lepidoptera ( Baker and Baker, 1983 ). Although Zhang and Saunders (2000) stated that “the small size of Burmannia flowers and the inaccessible anthers preclude wind-pollination or pollination by Lepidoptera or birds”, our data allow to refute this idea at least regarding Lepidoptera.…”

“…There are only a few reports of direct field observations of the anthesis in representatives of Burmannia . No floral visitors were detected during observations on B. chinensis and B. wallichii ( Zhang, 1999 ; Zhang and Saunders, 2000 ), whereas flowers of B. lutescens were visited by Culicidae (mosquitoes), Diptera, which were regarded as its potential pollinators ( Kato, 1996 ; Momose et al., 1998 ). In particular, Kato (1996) reported B. lutescens to be visited by mosquitoes from the genera Armigeres and Culex , whose proboscises correspond to the width of the openings between stigma and stamens and to the depth of the floral tube.…”

Structure and Development of Flowers and Inflorescences in Burmannia (Burmanniaceae, Dioscoreales)

“…(Ernst and Bernard, 1912) and B. wallichii (Miers) Hook.f. (Zhang and Saunders, 2000). Burmannia coelestis is reported to be apomictic (Ernst, 1909).…”