Conventional alternation of generations

The phenomena of apogamy and apospory, although easily induced and in some taxa the norm, have little impact on alternation of generations in the vast majority of lycophytes and ferns. The life cycle shown in Figure 2.2 shows the structures more conventionally concerned with alternation of generations in bracken fern, and which we can use as the basis of a consideration of the process in non-apogamous lycophytes and ferns. The reason for choosing bracken is that we know more about this fern...

Obligate apogamy

Dryopteris affinis ssp. affinis needs no prompting to generate sporophytes apogamously, but we know that their induction is stimulated by auxins and gibberellins (Menendez et al., 2006). In common with many other apogamous species, this taxon is widely distributed and very successful. Bommeria pedata, for example, has a considerably more extensive distribution than most of its sexually reproducing congeners (Gastony and Haufler, 1976). It is usually held that the reason for this success is that...

Induction of chloroplast movement

When part of a long protonemal cell (Yatsuhashi et al., 1985) or a two-dimensional gametophyte (Kagawa and Wada, 1994) was irradiated with a red or blue light microbeam (either slit, spot, or rectangular in shape, from a few micrometers to 10 or 15 m in diameter) at a weak fluence rate (e.g., 1 W m-2), chloroplasts outside the beam moved towards the light irradiated area. When the fluence rate of blue light was increased above 10 W m-2, chloroplasts moved away from the beam. Red light does not...

Spore release and dispersal

Discuss The Spore Dispersal Ferns

Once spores have been formed, it stands to reason that they can only effect the next stage in the alternation process if they are released, dispersed, and alight somewhere conducive to germination and gametophyte growth. This presents a huge challenge for propagules that lack vectors which target such sites (cf. flowering plants with insect pollinators). There is scant evidence for productive interactions between animal vectors and fern spores, but very little study of this seems to have been...

Evolution of roots

Nothing is known about the evolutionary origin of roots. Recent molecular genetics shows that angiosperm RAMs and SAMs are controlled by similar mechanisms to maintain stem cell populations, suggesting that roots may be derived from a developmental program associated with the SAM (references cited in Friedman et al., 2004), but genetic data are lacking for fern and lyco-phyte roots. Roots are similarly endogenous in ferns and lycophytes, regardless of whether they branch endogenously (ferns) or...

Climate change

Responses of ferns and lycophytes to global climate change are difficult to predict and have been little studied. Because spores provide ferns and lyco-phytes with superior long-distance dispersal capabilities, these groups may have an advantage over seed-bearing plants in adapting to climate changes Given, 1993 . However, increased habitat fragmentation, physiological stress, and habitat disturbance may cause local or global extinctions of fern and lycophyte species that are unable to survive...

Restoration

The role of natural disturbances at multiple scales has been important for fern and lycophyte regeneration processes and in maintenance of fern and lycophyte diversity Arens and Baracaldo, 1998 Page, 2002 . Ferns can also dominate degraded sites and impose barriers for tree regeneration by competing for soil moisture, nutrients, and light George and Bazzaz, 1999 Ashton et al., 2001 Slocum et al., 2004 . Slocum et al. 2004 found that clearing fern thickets caused rapid recruitment of woody...

Ex situ banking of spores

In contrast to the ex situ cultivation of whole plants, the banking of spores can preserve thousands of genotypes in much less space than is needed to grow one plant. In many ways similar to seed banking, traditional spore banking is based on the capacity of spores to remain viable through extreme desiccation. Many spores undergo drying in nature when they are dispersed and can survive in that state for from several days to many years, depending on the species. This has formed the basis for the...

Three evolutionary radiations ofhomosporous leptosporangiate ferns

Paleobotanical studies reveal a pattern of leptosporangiate evolution in which there have been three major pulses of evolutionary radiation Rothwell, 1987 . Diversity among the Paleozoic fossils is summarized by Stewart and Rothwell 1993 , whereas the Mesozoic and Cenozoic records of ferns recently have been compiled by Skog 2001 and Collinson 2001 respectively. Pulses of filicalean evolution were first recognized by Lovis 1977 , who concluded correctly that the species richness of filicaleans...