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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.
Plants that are homosporous produce spores of the same size and type. Heterosporous plants, such as seed plants , spikemosses , quillworts , and ferns of the order Salviniales produce spores of two different sizes: the larger spore (megaspore) in effect functioning as a "female" spore and the smaller (microspore) functioning as a "male".
The leaves contain a single, unbranched vascular strand, and are microphylls by definition. [6] They are usually arranged in spirals. [ 7 ] The kidney-shaped (reniform) spore -cases ( sporangia ) contain spores of one kind only, ( isosporous, homosporous ), and are borne on the upper surface of the leaf blade of specialized leaves (sporophylls ...
The moss life-cycle starts with a haploid spore that germinates to produce a protonema (pl. protonemata), which is either a mass of thread-like filaments or thalloid (flat and thallus-like). Massed moss protonemata typically look like a thin green felt, and may grow on damp soil, tree bark, rocks, concrete, or almost any other reasonably stable ...
Most heterosporous plants there are two kinds of sporangia, termed microsporangia and megasporangia. Sporangia (clustered in sori) on a fern leaf Equisetum arvense strobilus cut open to reveal sporangia. Sporangia can be terminal (on the tips) or lateral (placed along the side) of stems or associated with leaves.
Some lycophytes are homosporous while others are heterosporous. [5] When broadly circumscribed , the lycophytes represent a line of evolution distinct from that leading to all other vascular plants , the euphyllophytes , such as ferns , gymnosperms and flowering plants .
Many club-moss gametophytes are mycoheterotrophic and long-lived, residing underground for several years before emerging from the ground and progressing to the sporophyte stage. [4] Lycopodiaceae and spikemosses (Selaginella) are the only vascular plants with biflagellate sperm, an ancestral trait in land plants otherwise only seen in bryophytes.
Young sporophytes of the common moss Tortula muralis. In mosses, the gametophyte is the dominant generation, while the sporophytes consist of sporangium-bearing stalks growing from the tips of the gametophytes Sporophytes of moss during spring In flowering plants, the sporophyte comprises the whole multicellular body except the pollen and ...