Bryophyte6 Maret 2010 pukul 04:23 | Ditulis dalam Uncategorized | Tinggalkan komentar
Bryophytes are all embryophytes (‘land plants’) that are non-vascular: they have tissues and enclosed reproductive systems, but they lack vascular tissue that circulates liquids. They neither have flowers nor produce seeds, reproducing via spores. The term bryophyte comes from Greek βρύον – bryon, “tree-moss, oyster-green” + φυτόν – fyton “plant”.
The bryophytes (or non-tracheophytes) do not form a monophyletic group but consist of three groups, the Marchantiophyta (liverworts), Anthocerotophyta (hornworts), and Bryophyta (mosses). Originally the three groups were brought together as the three classes of division Bryophyta. However, since the three groups of bryophytes form a paraphyletic group, they now are placed in three separate divisions.
Modern studies of the land plants generally show one of two patterns.
- In one of these patterns, the liverworts were the first to diverge, followed by the hornworts, while the mosses are the closest living relatives of the polysporangiates (which include the vascular plants).
- In the other pattern, the hornworts were the first to diverge, followed by the vascular plants, while the mosses are the closest living relatives of the liverworts.
These plants are generally gametophyte-oriented; that is, the normal plant is the haploid gametophyte, with the only diploid structure being the sporangium in season. As a result, bryophyte sexuality is very different from that of other plants. There are two basic categories of sexuality in bryophytes:
- Dioicous bryophytes produce only antheridia (male organs) or archegonia (female organs) on a single plant body.
- Monoicous bryophytes produce both antheridia and archegonia on the same plant body.
Some bryophyte species may be either monoicous or dioicous depending on environmental conditions. Other species grow exclusively with one type of sexuality.
Notice that these terms are not the same as monoecious and dioecious, which refer to whether or not a sporophyte plant bears one or both kinds of gametophyte. Those terms apply only to seed plants.
Bryophyte life cycle
Dispersal in bryophytes is via spores; they neither have flowers nor produce seeds. Bryophytes do produce gametes that fuse to form a zygote, which in turn develops into an embryo, but this is not contained in a seed as in gymnosperms and angiosperms.