Showing posts with label Reproduction. Show all posts
Showing posts with label Reproduction. Show all posts

Sunday, August 10, 2008

Lycopodium clavatum

Lycopodium clavatum (running clubmoss) - Lycopodiaceae. An example of a seedless vascular plant - so reproduces by spore similar to liverworts but also has true conductive tissues, xylem and phloem. Unlike the liverworts, club mosses are homosporous (have only one kind of spore) and spores give rise to bisexual gametophytes.
The above ground portion pictured rather blurrily above is the rhizome. The gametophytes of some club mosses, including this species, grow below ground, are non-photosynthetic and maintain a mycorrhizal relationship with fungi. Strobili are borne on aerial stems attached to the rhizomes (pictured at left). Strobilus (pl. strobili) = a cone-like cluster of sporophylls on an axis. Sporangium borne on the strobili release spores that develop into the gametophyte which bear both archegonia and antheridia. During fertilization, biflagellated sperm produced by the antheridium swim to the egg produced by the archegonium (the presence of water is required). The newly produced sporophyte may remain attached to the gametophyte for a long time but eventually detaches to become a separate individual. (Plant Biology - Raven, Evert, Eichhorn)

Monday, August 4, 2008

Liverworts


Marchantia polymorpha (lung liverwort) - Marchantiaceae: a thalose liverwort/hepatic, pictured above surrounded by moss. Liverworts do not possess stomata and are non-vascular (except for water-conducting strands in the gametophytes of a few genera which I feel like I observed when pulling the archegoniophore apart from the gametophyte of this species) and reproduce by spore. Liverworts are a member of the Marchantiophyta division, part of the Bryophytes.

Because liverworts are non-vascular they do not possess real roots but rather rhizoids. Rhizoid = a root-like structure lacking conductive tissue (xylem and phloem). The archegonia are pictured above, these are the female reproductive structures - motile sperm from the male gametophyte (antheridiophore) are splash-dispersed to the female. Fertilization occurs leading to a zygote > an embryo > a young sporophyte. Spores are eventually released from the mature sporophyte and would be located on the underside of the archegoniophore as pictured below (mature sporophytes aren't visible and probably already dispersed).
Marchantia also conducts asexual reproduction through gemma cups on the leaves - a gemma cup is visible in the first photograph on the lower-most leaf pictured. Gemmae are splash-dispersed from the gemma cup onto soil and clones result. Gemma (pl. gemmae) = a bud or bud-like structure, or cluster of cells which separate from the parent plant and propagate offspring plants.