Search results
Results from the WOW.Com Content Network
Club-mosses (Lycopodiales) are homosporous, but the genera Selaginella (spikemosses) and Isoetes (quillworts) are heterosporous, with female spores larger than the male. [2] As a result of fertilisation, the female gametophyte produces sporophytes.
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".
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.
Among the lycophytes, both Isoetes and the Selaginellaceae (spikemosses) are heterosporous, while the remaining lycophyte family Lycopodiaceae (clubmosses) is homosporous. [16] As heterosporous plants, fertile Isoetes sporophytes produce megaspores and microspores, which develop in the megasporangia and microsporangia. [17]
The kidney-shaped (reniform) spore-cases contain spores of one kind only, (isosporous, homosporous), and are borne on the upper surface of the leaf blade of specialized leaves (sporophylls) arranged in a cone-like strobilus at the end of upright stems. [6] Each sporangium contains numerous small spores. [7]
Land plants all have heteromorphic (anisomorphic) alternation of generations, in which the sporophyte and gametophyte are distinctly different. All bryophytes, i.e. liverworts, mosses and hornworts, have the gametophyte generation as the most conspicuous. As an illustration, consider a monoicous moss.
Lycopodiaceae (homosporous lycophytes) split off from the branch leading to Selaginella and Isoetes (heterosporous lycophytes) about ~400 million years ago, during the early Devonian. The two subfamilies Lycopodioideae and Huperzioideae diverged ~350 million years ago, but has evolved so slowly that about 30% of their genes are still in ...