Myriopteris aurea (Poir.) Grusz & Windham

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Myriopteris aurea, the golden lip fern or Bonaire lip fern, is a moderately-sized fern native to the Americas, a member of the family Pteridaceae. Unlike many members of its genus, its leaf is only modestly dissected into lobed leaflets (pinnae), which are hairy both above and below. One of the cheilanthoid ferns, until 2013 it was classified in the genus Cheilanthes as Cheilanthes bonariensis, when the genus Myriopteris was again recognized as separate from Cheilanthes. It typically grows on dry, rocky slopes, and ranges from Mexico, where it is common and widespread, and the southwestern United States south and east through Central and South America as far as Chile and Argentina.

Description

Leaf bases are closely spaced along the horizontal rhizome, which is variously described as being 3 millimeters (0.1 in) or 4 to 8 millimeters (0.2 to 0.3 in) in diameter. The rhizome bears scales, which are linear to lanceolate, with untoothed or very slightly toothed margins. They are bi-colored, with a shiny central stripe red-brown or shiny chestnut-brown to black in color and narrow light-brown margins, and measure 3 millimeters (0.1 in) long. They are slightly twisted and strongly pressed against the rhizome.

The fronds spring up in clusters; unlike many ferns, they do not unfold as fiddleheads (noncircinate vernation).  They range from 10 to 60 centimeters (3.9 to 24 in) long, sometimes up to 75 centimeters (30 in), and are 0.5 to 3.5 centimeters (0.20 to 1.4 in) broad. The stipe (the stalk of the leaf, below the blade) represents from one-sixth to one-third of the total length of the leaf, and is 3 to 15 centimeters (1.2 to 5.9 in) long. The upper surface of the stipe is rounded and not grooved. The stipe is shiny, dark chestnut brown to black or purplish-black in color. It is covered in straight, white to tan hairs, 2 millimeters (0.08 in) long and more or less pressed against the stipe.

The leaf blades are linear to lanceolate or elliptical, and pinnate-pinnatifid (cut into deeply lobed pinnae), much less dissected than most Myriopteris species. It is from 1 to 4 centimeters (0.4 to 2 in) wide. The rachis (leaf axis) is densely covered in pubescent hairs, but lacks scales. From 15 to 44 pairs of pinnae are present, attached directly to the rachis or with a short stalk. Each pinna is approximately equilateral in shape, has from 3 to 8 pairs of lobes, which may be cut as shallowly as one-fourth or as deeply as three-fourths of the distance to the costa (pinna axis). The number of lobes and deepness of cutting can vary a great deal between individuals. They are joined to the rachis by a distinct stalk; the dark color of the rachis extends into the stalk but terminates abruptly in a swollen node covered with hairs. The lowest pair of pinnae is slightly smaller than the one above. At the other end of the frond, the pinnae gradually taper to an acute or obtuse apex. The leaf tissue is parchment-like to almost leathery. The upper surface of the pinnae is covered with scattered to abundant hairs, stiff, flattened against the surface, one-celled, and about 2 millimeters (0.08 in) long. They are pale golden-tan in color. The lower surface of the pinnae is also covered in hairs, matted so thickly as to hide the leaf tissue, which vary from white, particularly when young, to rusty red in color. They do not curl up when dried out.

On fertile fronds, the sori are located at the ends of veins near the margin of the leaf, forming a more or less continuous zone adjacent to the margin, which curls back slightly but does not form a distinct false indusium to protect them. The recurved margin is 0.05 to 0.25 millimeters (0.0020 to 0.0098 in) wide. It is somewhat thinner and more delicate than the rest of the leaf tissue, though not quite hyaline. Each sporangium contains 32 dark brown to black spores. The vast majority of M. aurea individuals thus far examined are apogamous triploids, with a chromosome number of 90 present in both sporophyte and gametophyte. A few populations forming 64 spores per sporangium have reportedly been found, and are presumed to be sexual diploids.

Among its congeners M. aurea is most similar to M. yatskievychiana, known only from Sonora which is smaller and has dense white (rather than rusty) hairs on the underside of the leaf. The pinnate-pinnatifid leaf blades distinguish these two species from the rest of the genus, the other species being more highly dissected. M. aurea superficially resembles some species of Astrolepis, such as A. sinuata, which have short, deeply lobed pinnae, but they bear the stellate scales that give their genus its name rather than the hairs seen on M. aurea. In the southern part of its range, it might be confused with Cheilanthes fraseri, but the latter has leaves widely spaced along the rhizome, pinnae more or less triangular (rather than equilateral), and rhizome scales light brown at the apex, rather than dark brown.

Myriopteris aurea - Wikipedia

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