Megaceros
Encyclopedia
Megaceros is a genus
of hornwort
s in the family Dendrocerotaceae
. The genus is found in the Old World tropics of east Asia
and Australia
. Its name means 'big horn', and refers both to the exceptionally large size of the gametophyte
thallus
and to the large, horn-shaped sporophyte
that the plants produce. Many species
have a branching thallus that is more than two centimeters wide. The gametophytes are monoicous
.
The genus Megaceros is unusual among hornworts in that the sporophyte
does not have stoma
ta, and the spore
s are green because they contain chloroplast
s, as does the related genus Dendroceros
. The thallus cells often contain more than one chloroplast, as opposed to other hornwort genera. The elater
s are helical.
The genus Megaceros was first recognized in 1907 by D. Campbell. More recently, the genera Nothoceros
and Phaeomegaceros
have been split off from this genus. The former genus includes all New World species previously included in Megaceros.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of hornwort
Hornwort
Hornworts are a group of bryophytes, or non-vascular plants, comprising the division Anthocerotophyta. The common name refers to the elongated horn-like structure, which is the sporophyte. The flattened, green plant body of a hornwort is the gametophyte plant.Hornworts may be found worldwide,...
s in the family Dendrocerotaceae
Dendrocerotaceae
The Dendrocerotaceae is the only family of hornworts in the order Dendrocerotales....
. The genus is found in the Old World tropics of east Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
and Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
. Its name means 'big horn', and refers both to the exceptionally large size of the gametophyte
Gametophyte
A gametophyte is the haploid, multicellular phase of plants and algae that undergo alternation of generations, with each of its cells containing only a single set of chromosomes....
thallus
Thallus (tissue)
Thallus, from Latinized Greek θαλλός , meaning a green shoot or twig, is the undifferentiated vegetative tissue of some organisms in diverse groups such as algae, fungus, some liverworts, lichens, and the Myxogastria. Many of these organisms were previously known as the thallophytes, a polyphyletic...
and to the large, horn-shaped sporophyte
Sporophyte
All land plants, and some algae, have life cycles in which a haploid gametophyte generation alternates with a diploid sporophyte, the generation of a plant or algae that has a double set of chromosomes. A multicellular sporophyte generation or phase is present in the life cycle of all land plants...
that the plants produce. Many species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
have a branching thallus that is more than two centimeters wide. The gametophytes are monoicous
Monoicous
Monoicous is a botanical term used to describe plants which bear both sperm and eggs on the same gametophyte. Dioicous is the complementary term describing species in which gametophytes produce only sperm or eggs but never both. The terms are used largely but not exclusively in the context of...
.
The genus Megaceros is unusual among hornworts in that the sporophyte
Sporophyte
All land plants, and some algae, have life cycles in which a haploid gametophyte generation alternates with a diploid sporophyte, the generation of a plant or algae that has a double set of chromosomes. A multicellular sporophyte generation or phase is present in the life cycle of all land plants...
does not have stoma
Stoma
In botany, a stoma is a pore, found in the leaf and stem epidermis that is used forgas exchange. The pore is bordered by a pair of specialized parenchyma cells known as guard cells that are responsible for regulating the size of the opening...
ta, and the spore
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
s are green because they contain chloroplast
Chloroplast
Chloroplasts are organelles found in plant cells and other eukaryotic organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve free energy in the form of ATP and reduce NADP to NADPH through a complex set of processes called photosynthesis.Chloroplasts are green...
s, as does the related genus Dendroceros
Dendroceros
Dendroceros is a genus of hornworts in the family Dendrocerotaceae. The genus contains about 51 species native to tropical and sub-tropical regions of the world.- Description :...
. The thallus cells often contain more than one chloroplast, as opposed to other hornwort genera. The elater
Elater
An elater is a cell that is hygroscopic, and therefore will change shape in response to changes in moisture in the environment. Elaters come in a variety of forms, but are always associated with plant spores...
s are helical.
The genus Megaceros was first recognized in 1907 by D. Campbell. More recently, the genera Nothoceros
Nothoceros
Nothoceros is a genus of hornworts in the family Dendrocerotaceae. The genus is found in New Zealand, South America, and neotropical and eastern North America....
and Phaeomegaceros
Phaeomegaceros
Phaeomegaceros is a genus of hornworts in the family Dendrocerotaceae. It includes seven species....
have been split off from this genus. The former genus includes all New World species previously included in Megaceros.