A gemma (plural ''gemmae'') is a single
cell
Cell most often refers to:
* Cell (biology), the functional basic unit of life
Cell may also refer to:
Locations
* Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery ...
, or a mass of cells, or a modified bud of tissue, that detaches from the parent and develops into a new individual. This type of asexual reproduction is referred to as
fragmentation. It is a means of
asexual propagation in
plant
Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclu ...
s. These structures are commonly found in
fungi
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
,
alga
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
e,
liverwort
The Marchantiophyta () are a division of non-vascular land plants commonly referred to as hepatics or liverworts. Like mosses and hornworts, they have a gametophyte-dominant life cycle, in which cells of the plant carry only a single set of ...
s and
mosses, but also in some
flowering plant
Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...
s such as pygmy
sundew
''Drosera'', which is commonly known as the sundews, is one of the largest genera of carnivorous plants, with at least 194 species. 2 volumes. These members of the family Droseraceae lure, capture, and digest insects using stalked mucilaginou ...
s and some species of
butterwort
''Pinguicula'', commonly known as the butterworts, is a genus of carnivorous flowering plants in the family Lentibulariaceae. They use sticky, glandular leaves to lure, trap, and digest insects in order to supplement the poor mineral nutrition ...
s.
Vascular plants have many other methods of asexual reproduction including
bulbils
A bulbil (also referred to as bulbel, bulblet, and/or pup) is a small, young plant that is reproduced vegetatively from axillary buds on the parent plant's stem or in place of a flower on an inflorescence. These young plants are clones of the p ...
and
turions.
In mosses and liverworts
The production of gemmae is a widespread means of asexual reproduction in both liverworts and mosses. In liverworts such as ''
Marchantia
''Marchantia'' is a genus of liverworts in the family Marchantiaceae and the order Marchantiales.
The thallus of ''Marchantia'' shows differentiation into two layers: an upper photosynthetic layer with a well-defined upper epidermis with por ...
'', the flattened plant body or thallus is a
haploid gametophyte
A gametophyte () is one of the two alternating multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has one set of chromosomes. The gametophyte is the ...
with gemma cups scattered about its upper surface. The gemma cups are cup-like structures containing gemmae. The gemmae are small discs of haploid tissue, and they directly give rise to new gametophytes. They are dispersed from gemma cups by rainfall.
[Smith, AJE (1989) ''The Liverworts of Britain and Ireland'', Cambridge University Press, Cambridge.]
The gemmae are bilaterally symmetrical and are not differentiated into dorsal and ventral surfaces. The mature gemmae fall on the ground and if conditions are suitable their germination starts immediately. The surface of the gemma which comes in contact of the soil gives out many rhizoids. This surface eventually becomes the lower(ventral) surface of the thallus. Meanwhile, the apical cells present in the two lateral notches become active and form two thalli in opposite directions.
References
External links
Marchantiales– diagrams and micrographs of liverwort gemmae
Plant morphology
Fungal morphology and anatomy
Plant reproduction
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