Asplenium rhizophyllum
| Asplenium rhizophyllum | |
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| Asplenium rhizophyllum on rocks in the Red River Gorge, Daniel Boone National Forest, Kentucky, USA. | |
| Scientific classification | |
| Kingdom: | Plantae |
| Division: | Pteridophyta |
| Class: | Polypodiopsida/Pteridopsida (disputed) |
| Order: | Polypodiales |
| Family: | Aspleniaceae |
| Genus: | Asplenium |
| Species: | A. rhizophyllum |
| Binomial name | |
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Asplenium rhizophyllum L. |
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| Synonyms | |
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Antigramma rhizophylla (L.) J.Sm. |
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Antigramma rhizophylla (L.) J.Sm.
Camptosorus rhizophyllus (L.) Link
Asplenium rhizophyllum, the (American) walking fern, is a frequently-occurring fern native to North America. It is a close relative of Asplenium ruprechtii (syn: Camptosorus sibiricus) which is found in East Asia and also goes by the common name of "walking fern".
Asplenium rhizophyllum is a small fern whose undivided, evergreen leaves and long, narrow leaf tips, sometimes curving back and rooting, give it a highly distinctive appearance. It grows in tufts, often surrounded by child plants formed from the leaf tips. The leaves of younger plants tend to lie flat to the ground, while older plants have leaves more erect or arching.
It does not spread and form new plants via the roots. Its rhizomes (underground stems) are upright or nearly so, short, about 1 millimetre (0.04 in) in diameter, and generally unbranched. They bear dark brown or blackish, narrowly triangular or lance-shaped scales which are strongly clathrate (bearing a lattice-like pattern). The scales are 2 to 3 millimetres (0.08 to 0.1 in) long and 0.5 to 1 millimetre (0.02 to 0.04 in) wide (occasionally as narrow as 0.2 millimetres (0.008 in)) with untoothed margins. The stipe (the part of the stem below the leaf blade) is 0.5 to 12 centimetres (0.20 to 4.7 in) long (occasionally up to 15 centimetres (5.9 in) long), and ranges from one-tenth to one and one-half times the length of the blade. The stipe is reddish-brown and sometimes shiny at the base, becoming green above, and narrowly winged. Scales like those of the rhizome are present at the stipe base, changing to tiny club-shaped hairs above.
The leaf blades are not subdivided, as in most other ferns, but are narrowly triangular to linear or lance-shaped. Their shape can be quite variable, even on the same plant. They measure from 1 to 30 centimetres (0.4 to 10 in) long and from 0.5 to 5 centimetres (0.2 to 2 in) across and have a leathery texture with sparse hairs, more abundant below than above. The rachis (leaf axis) is dull green in color and almost devoid of hairs. On the underside of the blade, the veins are difficult to see and anastomose (split and rejoin each other), forming a series of areoles (the small areas enclosed by the veins) near the rachis. Fertile fronds are usually larger than sterile fronds, but their shape is otherwise the same. The base of the blade is typically heart-shaped (with the stipe protruding from the cleft); the bulges on either side of the cleft are frequently enlarged into auricles (rounded lobes), or occasionally into sharply-pointed, tapering lobes. The leaf tips may be rounded but are typically very long and attenuate (drawn out); the attenuate tips are capable of sprouting roots and growing into a new plant when the tip touches a surface suitable for growth. On rare occasions, the auricles at the leaf base will also take on an attenuate shape and form roots at the tip. The ability of the leaf tips to root and form a new plant at some distance from the parent gives the species its common name. The young leaves forming from a bud at the leaf tip are round to pointed at their apex, not yet having developed the long-attenuate shape.
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Wikipedia