Dust seed production and dispersal in Swedish Pyroleae species

Abstract

Dust seeds are the smallest seeds in angiosperms weighing just about a few micrograms. Th ese seeds are characteristic of most orchids, and several studies have been performed on seed features, fecundity and dispersal of orchid dust seeds. In this study we examine seed features, seed production and seed dispersal in another plant group with dust seeds, the Pyroleae (Monotropoideae, Ericaceae), focusing on six species: Pyrola chlorantha , P. minor , P. rotundifolia , Chimaphila umbellata , Moneses unifl ora and Orthilia secunda . Seed production per capsule among these species was in the range between ca 1000 and 7800, and seed production per capsule bearing shoot was in the range between ca 7000 and 60 000. Combining our results with published information on pollen-ovule ratios suggests that these Pyroleae species have a generally effi cient pollination system. Th e most fecund species was P. minor , the only species among the investigated that is probably largely self-pollinating. Th e investigated Pyroleae species have a seed production comparable to the less fecund orchid species. We studied seed dispersal in the fi eld in one of the species, P. chlorantha . Despite the extremely small and potentially buoyant seeds, the vast majority of seeds are deposited close to the seed source, within a few meters. Further studies on the recruitment ecology of the investigated Pyroleae species are currently under way.

Specificity of fungal associations of Pyroleae and Monotropa hypopitys during germination and seedling development

“…Seed production per capsule is on average 7800 in C. umbellata , 7000 in Moneses uniflora and 2500–3000 in the two Pyrola species (Johansson et al . ). Seed production in M. hypopitys has, to our knowledge, not been investigated.…”

Seed dispersal in six species of terrestrial orchids in Biebrza National Park (NE Poland)

“…Machon et al [47] found that 95% of Spiranthes spiralis seeds were trapped less than 1.35 m from infructescences, and 50% were noted within 5 cm of the nearest fruiting plants. In other plants with dust seeds, for example from the genus Pyrola, the vast majority of seeds are deposited close to the seed source [42]. Short-distance dispersal of orchid seeds is also suggested in studies presenting and interpreting results of population genetic variation [12,13,27,54].…”

“…40 km) by air and to be among the first plants to colonize the island after the 1883 eruption. Besides seed properties, vegetation type, wind characteristics, and plant size are the most often considered factors influencing dispersal distance in species with dust seeds [16,[40][41][42]. Although some authors have stated that information about long-distance dispersal over more than 10-15 km should be regarded as extremely rare [43], it is often reported in orchid literature [28,33,38].…”

The latest news from biological interactions in orchids: in love, head to toe

“…One can even speculate that the joint evolution of these traits allowed orchids, one of the largest plant families with 27 000 species, to undergo greater diversification than families displaying symbiotic germination or pollinia dispersal alone. Interestingly, pyroloids, a tribe of Ericaceae with small seeds, symbiotic germination (Hashimoto et al ., ) and large seed production (Johansson et al ., ), also tend to transfer pollen clusters by way of insects, that is, in tetrads or even larger aggregates (Takahashi, ). This striking convergence suggests that symbiotic germination and transfer of pollen aggregates sometimes reinforce each other in evolution.…”