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Seed morphology and its numerical analysis of the 9 taxa belonging to the family Urticaceae carried out with the help of scanning electron microscopy. Seed micro and macro morphological characters were significantly helpful to trace the phenetic relationship between the taxa of the family Urticaceae.
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Citations
‘Dust seeds’ with an undifferentiated (organless) embryo are known to be produced by mycoheterotrophic species (MH) in nine families of angiosperms. However, aside from the numerous studies on seed germination of orchids, relatively little is known about germination in MH families. In the Ericaceae, some degree of mycoheterotrophy (full, partial or initial) and dust seeds with an undifferentiated embryo occur in all species in the three tribes of Monotropoideae, the only subfamily of Ericaceae with this combination of characters. In most species, the seed is <0.90 mm in the greatest dimension, the endosperm is absent ( Pityopus ) or consists of few to many (30–40) cells, and the embryo is minute, consisting of as few as two cells in Monotropa . Germination in Monotropoideae is monopolar, with only the radicular pole of the embryo participating in germination. Thus, germination polarity differs from that of the dust seeds of orchids in which only the plumular pole of the embryo (protocorm) participates in germination. The dust seeds in Monotropoideae require the presence of fungi, either direct contact with a fungus or the presence of a diffusible substance therefrom, to germinate (symbiotic germination). Recently, representatives of the four genera of tribe Pyroleae have been successfully germinated asymbiotically in vitro . We present a broad overview of dust-size seeds in angiosperms and conclude that they should be subdivided into at least two major categories.
Micromorphology of seeds and pollen of Orobanche alsatica, O. bartlingii and O. mayeri, the central European representatives of the O. alsatica aggregate (Orobanchaceae) was investigated on the basis of 32 samples from 18 localities in Poland, Slovakia, Czech Republic, Austria, Bosnia and Herzegovina, and Russia. Concerning seeds, the best taxonomic character is a narrow trough on external sides of radial walls of cells of the seed wall, which is always present and continuous in O. bartlingii, mostly absent in O. mayeri, and mostly present solely at wall segment junctions (vertices) in O. alsatica (individuals parasitising Peucedanum spp.; continuous in parasites of Seseli osseum). As for pollen, the exine sculpture is verrucate in O. mayeri, granulate in O. bartlingii, and granulate to scabrate in O. alsatica. O. alsatica parasitising Peucedanum spp. and Seseli osseum (host-related morphotypes) differ in seed shape, ornamentation and wall-perforation diameter. Variability of seed and pollen characters is high, and identical morphologies occur among the investigated species. The variation coefficient is too strongly correlated with the sample size to be a reliable estimator the taxonomic value of a character. Differences in seed and pollen sculpture, hosts and ecological preferences confirm the separation of the three examined taxa at species level.
