Polypodium appalachianum
Encyclopedia
Polypodium appalachianum is a recently-recognized fern species, native to eastern North America. Sometimes called the Appalachian rockcap fern, it is very similar in appearance to Polypodium virginianum
. For years, P. virginianum -- long considered a variety of the British Polypodium vulgare
-- was recognized as having cryptic races, with diploid, triploid, and tetraploid representatives. Since the triploid specimens bore abortive spores, it was apparently the hybrid between the diploid and tetraploid groups. In 1991, it was resolved that the type of P. virginianum was the tetraploid series, and that it is an allotetraploid species of hybrid origin, with the diploid species as one parent. The diploid species was then named P. appalachianum. The other parent of P. virginianum was found to be Polypodium sibiricum. Interestingly, the tetraploid of hybrid derivation tolerates warmer climates than either parent.
P. appalachianum is an epipetric plant, preferring sandstone or other hard, noncalcareous rocks. However, it is known to grow as an epiphyte
in the Smoky Mountains. Throughout much of its range, it will be found to grow in places more sheltered from the sun and heat than is P. virginianum. Both species, and their hybrid, can form large clonal colonies, forming dense mats that hold organic matter in place on rock shelves and surfaces.
Polypodium virginianum
Polypodium virginianum, commonly known as Rock Polypody, Rock Cap Fern, or Common Polypody, is a small evergreen species of fern native to the Eastern United States and Canada...
. For years, P. virginianum -- long considered a variety of the British Polypodium vulgare
Polypodium vulgare
Polypodium vulgare, the common polypody, is a fern of the Polypodiaceae family.- Description :Polypodium vulgare, the common polypody, is a fern developing in isolation from along a horizontal rhizome. The fronds with triangular leaflets measure 10 to 50 centimetres...
-- was recognized as having cryptic races, with diploid, triploid, and tetraploid representatives. Since the triploid specimens bore abortive spores, it was apparently the hybrid between the diploid and tetraploid groups. In 1991, it was resolved that the type of P. virginianum was the tetraploid series, and that it is an allotetraploid species of hybrid origin, with the diploid species as one parent. The diploid species was then named P. appalachianum. The other parent of P. virginianum was found to be Polypodium sibiricum. Interestingly, the tetraploid of hybrid derivation tolerates warmer climates than either parent.
| Character | P. appalachianum | P. virginianum |
|---|---|---|
| Frond shape | Widest near bottom | Widest in middle |
| Pinnule shape | Narrow, more nearly pointed | Broader, more rounded |
| Basal pinnule notch | Present | Absent |
P. appalachianum is an epipetric plant, preferring sandstone or other hard, noncalcareous rocks. However, it is known to grow as an epiphyte
Epiphyte
An epiphyte is a plant that grows upon another plant non-parasitically or sometimes upon some other object , derives its moisture and nutrients from the air and rain and sometimes from debris accumulating around it, and is found in the temperate zone and in the...
in the Smoky Mountains. Throughout much of its range, it will be found to grow in places more sheltered from the sun and heat than is P. virginianum. Both species, and their hybrid, can form large clonal colonies, forming dense mats that hold organic matter in place on rock shelves and surfaces.