Plant Reproduction

As you may recall, the information provided on plant diversity included information on plant reproduction because that is the basis of how plants were divided into the four groups. While all plants follow the alternation of generations pattern, each group has differences -- Bryophytes (nonvascular plants), Ferns (seedless vascular plants), Gymnosperms (cone bearing seed plants), and Angiosperms (flowering plants). Here is additional information using some different web sites for variety.

From a reproductive viewpoint, the primary issue for bryophytes is that the sperm is generally flagellated and requires free water in order to swim to the egg. This certainly limits the environments within which they can successfully reproduce. As you recall, the haploid generation is dominant in the bryophytes. The following web site from the University of the West Indies (Links to an external site.)addresses all “primitive” plants and we will return to it in the next section on ferns.

Ferns are vascular and thus grow to much larger size than bryophytes. The two generations live independently (mosses had the sporophyte dependent on the gametophyte and both gymnosperms and angiosperms have the gametophyte dependent on the sporophyte). They still rely on the sperm to swim through water to get to the egg. As a result they are dependent on free water to reproduce. This site from the US Forest Service addresses fern reproduction.

The major advance here is a seed and pollen. Seeds provide the embryonic sporophyte with protection and most gymnosperm seeds are modified for wind distribution. Pollen allows fertilization in the absence of free water and greatly expands the ecological habitats in which these plants can survive. In gymnosperms, pollen transfer is primarily by wind and gravity. As result, large amounts of pollen are produced. This McDaniel College site discusses gymnosperms (conifers in particular) and includes life cycle information. It also has a comparison of gymnosperms and angiosperms at the bottom of the page. It also has links to some lesser known gymnosperms. 

The angiosperms have dominated the earth since they arose. They produce flowers which entice animals to transfer pollen for them. This is a much more efficient approach and generally less pollen is needed. There are angiosperms that still use wind pollination (grasses, ragweed). In addition, the seed is enclosed in a fruit that attracts animals to feed on it and then distribute the seeds in their feces. Again, some seeds are modified for wind distribution or to stick to animals and fall off later. This McDaniel College site discusses flowers and includes life cycle information.  Here is additional information on seed dispersal from the Missouri Botanical Garden and from the Seed Site in Britain. Vanderbilt University has a large number of seed images as well.