Ophioglossum


Ophioglossum, the adder's-tongue ferns, is a genus of about 50 species of ferns in the family Ophioglossaceae. The genus name comes from Ancient Greek ὄφις, meaning "snake", and γλῶσσα, meaning "tongue". Their cosmopolitan distribution is mainly in tropical and subtropical habitats.
The genus has the largest number of chromosomes in the known plant kingdom, but contrary to popular belief does not have the largest number of chromosomes out of all known organisms, falling short to the protist Sterkiella histriomuscorum.

Description

Adders-tongues are so-called because the spore-bearing stalk is thought to resemble a snake's tongue. Each plant typically sends up a small, undivided leaf blade with netted venation, and the spore stalk forks from the leaf stalk, terminating in sporangia which are partially concealed within a structure with slit sides.
When the leaf blade is present, there is not always a spore stalk present, and the plants do not always send up a leaf, sometimes going for a year to a period of years living only under the soil, nourished by association with soil fungi.
The plant grows from a central, budding, fleshy structure with fleshy, radiating roots.
Ophioglossum malviae is known as the world's smallest terrestrial fern.

Taxonomy

Ophioglossum has a high chromosome count in comparison to other species, with 120 or up to 720 chromosomes possible in intervals of 120 due to polyploidy. It has almost 1260 number of chromosomes in the meiocyte which undergo meiosis, the reduction division to form the spore with only one set of chromosomes getting incorporated into each spore. The species Ophioglossum reticulatum has the highest number of chromosomes found in any multicellular organism.

Taxonomy

The Smith et al. classification of 2006, based on molecular phylogeny, placed Ophioglossum in Ophioglossaceae. Subsequent classifications have maintained this placement. Circumscriptions of the genus vary. The Christenhusz and Chase classification of 2014 includes Cheiroglossa and Ophioderma within Ophioglossum. This circumscription corresponds to subfamily Ophioglossoideae in the PPG I classification, which recognizes Cheiroglossa, Ophioderma, and Rhizoglossum as separate genera. More recently, it has been proposed to subdivide Ophioglossum more narrowly, removing a number of species into the new genera Goswamia, Haukia, and Whittieria.

Phylogeny

Phylogeny of Ophioglossum
Unassigned species:
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Species that may be placed in this genus include: