Ophioglossum, the adder's-tongue ferns, is a genus of about 25-30 species of ferns in the family Ophioglossaceae, of the order Ophioglossales. The name Ophioglossum comes from the Greek, and means "snake-tongue". 
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 slitted 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.
Species of Ophioglossum include:
- Ophioglossum austroasiaticum
- Ophioglossum azoricum
- Ophioglossum californicum
- Ophioglossum costatum
- Ophioglossum crotalophoroides
- Ophioglossum engelmannii
- Ophioglossum lusitanicum
- Ophioglossum nudicaule
- Ophioglossum pedunculosum
- Ophioglossum petiolatum
- Ophioglossum polyphyllum
- Ophioglossum pusillum
- Ophioglossum pycnosticum
- Ophioglossum reticulatum
- Ophioglossum tenerum
- Ophioglossum thermale
- Ophioglossum vulgatum
- eFloras: Ophioglossum . accessed 2.14.2014.
- Gerardus J. H. Grubben (2004). Vegetables. PROTA. p. 404. ISBN 978-90-5782-147-9. Retrieved 10 March 2013.
- Biomysteries Blog: "Largest Chromosome number of Ophioglossum"
- Flora of North America: Ophioglossum (Adder's-tongue)
- "The English Physician" by Culpeper: "Adder's Serpent" — description in 1814 herbalism book.
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