Developmental Problems in Selaginella (Selaginellaceae) in an Evolutionary Context

Abstract

The antiquity and diversity of Selaginella species attest to the evolutionary success of the genus. This success may be attributed, in part, to certain morphological and anatomical features that characterize Selaginella. Recent developmental studies of anisophylly, monoplastidy, the ligule, the rhizophore, marginal warty cells, and marginal teeth of the leaves, as well as aspects of the heterosporous life cycle are discussed. Unresolved questions concernmg vegetative features include the function of the ligule, morphological interpretation of the so-called rhizophore, and a possible role of distinctive leaf ornamentations In water economy. Among unresolved questions concerning reproduc ive morphology are the basis of heterospory, control of sporangial development, spore dispersal mechanisms as they anec inbreeding and outcrossing, and other details of the reproductive process. It is concluded that the genus belagine offers numerous opportunities for future research.From the standpoint of both development and Selaginella are far from obvious. It is my contenevolution, the genus Selaginella raises a number tion that, at least in part, the reasons may be foun of intriguing questions. In this regard the following quotation from Bierhorst (1971) seems appropriate: unique and reproductive features. These include amsophylly, the ligule, the presence of certain foliar â"¢ f ., c 1 • II â-I J c 7 • rf J epidermal ornamentations, the aerial root (rhizo-Ihe lamiiy belagmellaceae mcludes belagineila and , v i i j * *^^t^ of the ^eral very closelv related fossil forms which are known P^ore), monoplastidy, and certam aspeciĥ eterosporous Hfe cycle (Fig. 1). It should be em-Selaginella is probably one of the oldest of all extant phasized that although each of these features may genera of vascular plants, second only to Lycopodium, ^^ f^^^^ -^ ^^j^^^. j^^^^ groups (for example, the Despite its great antiquity, which might lead one to v i • r j • r . n oc in Spladnella), expect specialization and relative genetic stagnation, ^^g^'^ '' ^^^^^ ^^ ^^^^^^^ ^' ""^^ ^^ ^ !Lne to several very closely related fossil forms which are known from Lower Carboniferous and more recent strata.' The author thanks M. J. Spring for preparing the illustrations in Figure 1. ,,.o ^043

Micromorphology of outer exospore coatings inSelaginellamegaspores

“…A number of researchers have studied the genus from different viewpoints, ranging from anatomical (Hebant & Lee, 1984) and morphological (Lyon, 1901;Horner & Arnott, 1963;Horner et al 1975;Dengler, 1983;Page, 1989;Webster, 1992) to palaeobotanical (Bek et al 2001;Cottnam et al 2000) and most recently to phylogenetic and taxonomic investigations (Korall et al 1999;Korall & Kenrick, 2002). Phylogenetic analyses of DNA sequence data agree that Lycophytes (including Selaginella, Isoetes Linnaeus and Huperzia Bernardi) form a distinct clade, branching off from other tracheophytes early in land plant evolution (Pryer et al 2001, Quandt et al 2004).…”

Palynology of the Toarcian–Aalenian Global Boundary Stratotype Section and Point (GSSP) at Fuentelsaz (Lower–Middle Jurassic, Iberian Range, Spain)

“…This is remarkable since acritarchs and dinofiagellate cysts are usually common and diverse in European jurassic marine rocks (Williams and Bujak, 1985;Stover et al, 1996;Fauconnier, 1997). Only the species Micrhystridium lymensis (Plate I, Fig.…”

“…However, some of them adapted to grow under much drier and stressed conditions, especially during the Mesozoic (Abbink, 1998). The first two mentioned species are related to members of the family Selaginellaceae, the representatives of which nowadays occupy a wide range of habitats from rainforests to deserts (Webster, 1992). Due to the general arid conditions that existed in the study zone, it is possible that their sellaginellous producers were adapted to resist dry environments.…”

Megaspore and microfossil assemblages reveal diverse herbaceous lycophytes in the Australian Early Jurassic flora

“…The record of Selaginella sp. from the Upper Jurassic Talbragar Fossil Fish Bed (White, 1981a, figure 53;Beattie & Avery, 2012, figure 9F) is dismissed, since this fossil lacks the leaf arrangement typical of that genus (Webster, 1992) and has cup-shaped reproductive structures (S. McLoughlin, pers. obs., August 2013).…”