''Megaceros'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

hornwort Hornworts are a group of non-vascular Embryophytes (land plants) constituting the division Anthocerotophyta (). The common name refers to the elongated horn-like structure, which is the sporophyte. As in mosses and liverworts, hornworts have a ...

s in the family

Dendrocerotaceae The Dendrocerotaceae is the only family of hornworts in the order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organizati ...

. The genus is found in the Old World tropics of east

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an ...

and Australia. Its name means 'big horn', and refers both to the exceptionally large size of the

gametophyte A gametophyte () is one of the two alternation of generations, alternating multicellular organism, multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has on ...

thallus Thallus (plural: thalli), from Latinized Greek (), meaning "a green shoot" or " twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. Many of these organisms ...

and to the large, horn-shaped sporophyte that the plants produce. Many

species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...

have a branching thallus that is more than two centimeters wide. The gametophytes are

monoicous Monoicy () is a sexual system in haploid plants (mainly bryophytes) where both sperm and eggs are produced on the same gametophyte, in contrast with dioicy, where each gametophyte produces only sperm or eggs but never both.Crandall-Stotler, B.J ...

. The genus ''Megaceros'' is unusual among hornworts in that the sporophyte does not have

stoma In botany, a stoma (from Greek ''στόμα'', "mouth", plural "stomata"), also called a stomate (plural "stomates"), is a pore found in the epidermis of leaves, stems, and other organs, that controls the rate of gas exchange. The pore is bo ...

ta, and the

spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, ...

s are green because they contain

chloroplast A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it ...

s, as does the related genus ''

Dendroceros ''Dendroceros'' is a genus of hornworts in the family Dendrocerotaceae.Renzaglia, Karen S. & Kevin C. Vaughn. (2000) "Anatomy, development and classification of hornworts", pages 1-20 ''in'' A. Jonathan Shaw & Bernard Goffinet (Eds.), ''Bryophyte ...

''. They can have as many as 14 chloroplasts per cell, the highest known number in hornworts.Bryophyte Biology
/ref> The

elater An elater is a cell (or structure attached to 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. In ...

s are

helical Helical may refer to: * Helix A helix () is a shape like a corkscrew or spiral staircase. It is a type of smooth space curve with tangent lines at a constant angle to a fixed axis. Helices are important in biology, as the DNA molecule is ...

. 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''.

References

* Parihar, N. S. (1961). ''An Introduction to Embryophyta, Volume I''. Allahbad: Central Book Depot.

External links

Megaceros in Australia

Name changes in Megaceros
{{Taxonbar, from=Q6808315 Hornworts Bryophyte genera