The leaves taper from a broad base to a pointed apex and have lamina that are only one-cell-layer thick. A hydroid-containing midvein often extends from the stem into the leaf. Near the base of the shoot, reddish-brown multicellular rhizoids emerge from the stem to anchor the moss to its substrate. Water and mineral nutrients required for the moss to grow are absorbed, not by the rhizoids, but rather by the thin leaves of the plant as rain water washes through the moss cushion.
As is typical of bryophytes, mosses produce large, multicellular sex organs for reproduction. Many bryophytes are unisexual, or sexually dioicous. In mosses male sex organs, called antheridia, are produced in clusters at the tips of shoots or branches on the male plants; female sex organs, the archegonia, are produced in similar fashion on female plants. Numerous motile sperm are produced by mitosis inside the brightly colored, club-shaped antheridia
| DISTINGUISHING CHARACTERISTICS OF MOSSES, LIVERWORTS, AND HORNWORTS |
| Characteristics | Mosses (Bryophyta) | Liverworts (Marchantiophyta) | Hornworts (Anthocerotophyta) |
| Protonema | Filamentous, forming many buds | Globose, forming one bud | Globose, forming one bud |
| Gametophyte form | Leafy shoot simple or with air chambers | Leafy shoot or thallus; thallus | Simple thallus |
|
| Leaf arrangement | Leaves in spirals | Leaves in three rows | Not Applicable |
| Leaf form | Leaves undivided, midvein present | Leaves divided into two-plus lobes, no midvein | Not Applicable |
| Special organelles | None | Oil bodies | Single plastids with pyrenoids |
| Water-conducting cells | Present in both gametophyte and sporophyte | Present only in a few simple thalloid forms | Absent |
| Rhizoids | Brown, multicellular | Hyaline, one-celled | Hyaline, one-celled |
| Gametangial position | Apical clusters (leafy forms) | Apical clusters (leafy forms) or on upper surface of thallus | Sunken in thallus, scattered |
| Stomates | Present on sporophyte capsule | Absent in both generations | Present in both sporophyte and gametophyte |
|
| Seta | Photosynthetic, emergent from gametophyte early in development | Hyaline, elongating just prior to spore release | Absent |
| Capsule | Complex with operculum, theca, and neck; of fixed size | Undifferentiated, spherical, or elongate; of fixed size | Undifferentiated, horn-shaped; growing continuously from a basal meristem |
| Sterile cells in capsule | Columella | Spirally thickened elaters | Columella and pseudoelaters |
| Capsule dehiscence | At operculum and peristome teeth | Into four valves | Into two valves |
while a single egg develops in the base of each vase-shaped archegonium.
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