Search results
Results from the WOW.Com Content Network
Heterospory evolved due to natural selection that favoured an increase in propagule size compared with the smaller spores of homosporous plants. [2] Heterosporous plants, similar to anisosporic plants [clarification needed], produce two different sized spores in separate sporangia that develop into separate male and female gametophytes.
The main difference between spores and seeds as ... either homosporous (or isosporous) or heterosporous. Plants that are homosporous produce spores of the same size ...
As an illustration, consider a monoicous moss. Antheridia and archegonia develop on the mature plant (the gametophyte). In the presence of water, the biflagellate sperm from the antheridia swim to the archegonia and fertilisation occurs, leading to the production of a diploid sporophyte. The sporophyte grows up from the archegonium.
Salviniales are all aquatic and differ from all other ferns in being heterosporous, meaning that they produce two different types of spore (megaspores and microspores) that develop into two different types of gametophyte (female and male gametophytes, respectively), and in that their gametophytes are endosporic, meaning that they never grow outside the spore wall and cannot become larger than ...
They included heterosporous water ferns (Salviniales) (placed in a separate subclass by Cronquist et al. due to their highly modified morphology) within the leptosporangiate ferns, which they elevated to the rank of class as the Polypodiopsida (published by Cronquist et al. to include all ferns).
Most non-vascular plants, as well as many lycophytes and most ferns, are homosporous (only one kind of spore is produced). Some lycophytes, such as the Selaginellaceae and Isoetaceae, [7]: 7 the extinct Lepidodendrales, [8] and ferns, such as the Marsileaceae and Salviniaceae are heterosporous (two kinds of spores are produced).
In heterosporous plants (water ferns, some lycophytes, as well as all gymnosperms and angiosperms), there are two distinct types of sporangia, each of which produces a single kind of spore that germinates to produce a single kind of gametophyte. However, not all heteromorphic gametophytes come from heterosporous plants.
Psilotum is a genus of fern-like vascular plants.It is one of two genera in the family Psilotaceae commonly known as whisk ferns, the other being Tmesipteris.Plants in these two genera were once thought to be descended from the earliest surviving vascular plants, but more recent phylogenies place them as basal ferns, as a sister group to Ophioglossales.