Isolation and culture of protoplasts from young sporophytes ofSalvinia natans aseptically obtained by co-culture of female and male gametophytes

Sporophytes were aseptically obtained by co-culture of female and male gametophytes derived from two types of spores (megaspores and microspores) of the heterosporous fernSalvinia natans All. Protoplasts isolated enzymatically from juvenile leaflets of sporophytes were cultured in a 1/10 Murashige and Skoog's medium containing 2.2 M naphthalene acetic acid, 2.2 M 6-benzyl-aminopurine, 0.35 M mannitol, and 0.05 M sucrose. Cell division took place within 6 days of culture, and cell-clusters composed of 9–10 cells were observed after 30 days of culture.Abbreviations BA 6-benzyl-aminopurine - MS Murashige and Skoog - NAA naphthaleneacetic acid     

On the possible occurrence of anisospory in some Hepaticae

PANT, D. D. & SINGH, R., 1989. On the possible occurrence of anisospory in some Hepaticae. Possible anisospory is reported for the first time in four species of Hepaticae, viz., Targionia indica Udar, Targionia hypophylla L., Cyathodium aureo-nitens Griff. (Mitt.), Cyathodium barodae Chavan. The report is based on observations of wide variations in size of spores comparable with those of anisosporous mosses of the family Orthotrichacae.     

Selective forces in the emergence of the seed habit

The evolution of the seed is one of the major events in the history of land plants. In this paper, we consider the suite of characters that define the seed habit, and discuss the probable selective pressures that produced each character. Our major conclusion is that most characters are a direct consequence of the origin of heterospory and of natural selection for propagules with larger food reserves.
Seeds are traditionally defined by the possession of integuments. However, some heterosporous pteridophytes possess integument-like structures. Therefore, integuments cannot explain the evolutionary success of seed plants. Rather, we believe that the decisive character in this success is related to pollination. Seed plants differ from other heterosporous lineages in the capture of microspores before dispersal of the 'megaspore'. Modern gymnosperms all possess mechanisms whereby the maternal sporophyte withholds resources from potential propagules that have not been pollinated and/or fertilized. This represents an increase in efficiency over Pteridophytic reproduction. Wind-pollination means the propagule is vulnerable to pathogens that mimic pollen, and pathogen pressures may have contributed to some seed characters.     

Assessing phylogenetic relationships in extant heterosporous ferns (Salviniales), with a focus on Pilularia and Salvinia

Heterosporous ferns (Salviniales) are a group of approximately 70 species that produce two types of spores (megaspores and microspores). Earlier broad‐scale phylogenetic studies on the order typically focused on one or, at most, two species per genus. In contrast, our study samples numerous species for each genus, wherever possible, accounting for almost half of the species diversity of the order. Our analyses resolve Marsileaceae, Salviniaceae and all of the component genera as monophyletic. Salviniaceae incorporate Salvinia and Azolla; in Marsileaceae, Marsilea is sister to the clade of Regnellidium and Pilularia– this latter clade is consistently resolved, but not always strongly supported. Our individual species‐level investigations for Pilularia and Salvinia, together with previously published studies on Marsilea and Azolla (Regnellidium is monotypic), provide phylogenies within all genera of heterosporous ferns. The Pilularia phylogeny reveals two groups: Group I includes the European taxa P. globulifera and P. minuta; Group II consists of P. americana, P. novae‐hollandiae and P. novae‐zelandiae from North America, Australia and New Zealand, respectively, and are morphologically difficult to distinguish. Based on their identical molecular sequences and morphology, we regard P. novae‐hollandiae and P. novae‐zelandiae to be conspecific; the name P. novae‐hollandiae has nomenclatural priority. The status of P. americana requires further investigation as it consists of two geographically and genetically distinct North American groups and also shows a high degree of sequence similarity to P. novae‐hollandiae. Salvinia also comprises biogeographically distinct units – a Eurasian group (S. natans and S. cucullata) and an American clade that includes the noxious weed S. molesta, as well as S. oblongifolia and S. minima. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 157 , 673–685.     

A Mid Devonian seed-megaspore from East Greenland and the origin of the seed plants

A new species of late Mid Devonian seed-megaspore from East Greenland is described and named as Spermasporites allenii . The formerly monotypic genus Spermasporites is emended to accommodate this new species. Rare specimens of S. allenii , with near complete sporangial contents, occur together with specimens showing proximally adhering microspores. These demonstrate that S. allenii was contained within a sporangium exhibiting extreme anisospory, which is interpreted here as functionally bisexual. This is a key element in understanding its reproductive function. The megaspore was shed along with some attached microspores giving it potential for both cross- and self-fertilization. This confers the advantages of heterospory without recourse to separate micro- and megasporangia. This provides a more likely mechanism for seed plant origin than the archaeopteridalean sporangium reduction model. Ultrastructural study of the megaspore wall confirms the progymnosperm affinity of S. allenii . Comparable forms include the Frasnian Spermasporites devonicus and the Famennian seed-megaspores isolated from Archaeosperma arnoldii .