Myriopteris aemula
Myriopteris aemula, the Texas lip fern or rival lip fern, is a moderately-sized fern of Texas and Mexico, a member of the family Pteridaceae. Unlike many members of its genus, its leaves have a few hairs on upper and lower surfaces, or lack them entirely. One of the cheilanthoid ferns, it was usually classified in the genus Cheilanthes until 2013, when the genus Myriopteris was again recognized as separate from Cheilanthes. It typically grows on limestone rock.
| Texas lip fern | |
|---|---|
Scientific classification  | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Class: | Polypodiopsida |
| Order: | Polypodiales |
| Family: | Pteridaceae |
| Genus: | Myriopteris |
| Species: | M. aemula |
| Binomial name | |
| Myriopteris aemula (Maxon) Grusz & Windham | |
| Synonyms | |
| |
Description
Leaf bases are closely spaced along the rhizome,[1] variously described as 1 to 2 millimeters (0.04 to 0.08 in)[2] or 4 to 7 millimeters (0.2 to 0.3 in) in diameter.[1] The rhizome bears persistent scales, which are linear to narrowly lance-shaped, straight or slightly twisted, and loosely pressed against the surface of the rhizome.[1] Their margins are untoothed.[2] They may be uniformly brown[1] or tan to orange-brown[2][3] in color, or be darker at their base,[1][2] particularly in the center.[3]
The fronds spring up in clusters;[4] they do not unfold as fiddleheads like typical ferns (noncircinate vernation). When mature, they are 10 to 55 centimeters (3.9 to 22 in) long[1][4][2] and 4 to 15 centimeters (2 to 6 in) wide.[1] The stipe (the stalk of the leaf, below the blade) is 6 to 16 centimeters (2.4 to 6.3 in) long,[3] representing one-third to one-half of the total length of the leaf.[2] The upper surface of the stipe is rounded, and it is black to dark brown in color,[1][4] or black to very dark purple.[2] It may be hairless, or bear a few hairs (long ones of 1 mm and short ones less than 0.1 mm) on the upper surface.[2][3]
The leaf blades range in shape from deltate (triangular, broadest at the base) to ovate (egg-shaped, widest near the base). The blade is usually tripinnate (cut into pinnae, pinnules, and pinnulets) to tripinnate-pinnatifid (with deeply lobed pinnulets) at the base,[1][4] or even quadripinnate.[2] The rachis (leaf axis) is rounded on the upper side. It bears twisted hairs tightly pressed to it on the upper side, and scattered, spreading, straight hairs on the lower side; no scales are present. The pinnae are not jointed at the base,[1][4] and the dark pigmentation of the rachis enters the edge of the pinnae.[1] The pinnae at the base of the leaf are slightly larger than the pinnae immediately above them[1][4] and the pinnae are somewhat asymmetric about the costa (pinna axis).[1] The basiscopic pinnules (pointing at the leaf base) are slightly larger and more deeply dissected than the acroscopic pinnules (pointing at the leaf tip).[2] The lowest pair of basiscopic pinnules closest to the stem are noticeably larger than adjacent pinnules[1][5][3] and thin in texture.[2] The upper and lower surfaces of the pinnae have a few soft hairs, 0.5–0.8 mm in length or none at all.[2][1] The costae are black on the upper side for most of their length[1] and lack scales beneath.[1][4] The pinnulets are elliptical to long-triangular,[1] and not bead-shaped as in some other species of Myriopteris.[1][4] They are cordate at the base and acute at the tip.[3] The largest pinnulets are 3 to 6 millimeters (0.12 to 0.24 in) long,[1][4] and have sparse white hairs on upper and lower surfaces, or lack hairs entirely.[1]
On fertile fronds, the sori are protected by false indusia formed by the edge of the leaf curling back over the underside. The false indusia are slightly differentiated from the rest of the leaf tissue, and are 0.05–0.3 mm wide.[1][2] The edges of the indusia are not toothed or lobed.[3] Beneath them, the sori are usually not continuous around the edge of the leaf, and are often concentrated on lateral lobes of the fertile pinnulets,[1] particularly at the ends of veins.[2] Each sporangium in a sorus carries 64 tan spores. Individual sporophytes are sexual diploids, with a diploid chromosome number of 2n = 58.[1][2]
Taxonomy
Myriopteris aemula was first described by William Ralph Maxon in 1908, as Cheilanthes aemula, based on material collected by Edward Palmer in 1907 from Ciudad Victoria. He distinguished it from Cheilanthes microphylla, found growing with it, by its greater degree of cutting and the triangular shape of the leaf blade.[6]
The development of molecular phylogenetic methods showed that the traditional circumscription of Cheilanthes, including that used by Maxon, is polyphyletic. Convergent evolution in arid environments is thought to be responsible for widespread homoplasy in the morphological characters traditionally used to classify it and the segregate genera that have sometimes been recognized. On the basis of molecular evidence, Amanda Grusz and Michael D. Windham revived the genus Myriopteris in 2013 for a group of species formerly placed in Cheilanthes. One of these was C. aemula, which thus became Myriopteris aemula.[7]
In 2018, Maarten J. M. Christenhusz transferred the species to Hemionitis as H. aemula, as part of a program to consolidate the cheilanthoid ferns into that genus.[8]
The common name "lip fern" comes from the position of the sporangia at the edge or lip of the leaf, typical of the genus.[9] This species is referred to as "rival lip fern", a translation of the specific epithet aemula (believed to refer to the "imitation" of the C. microphylla found growing with it)[4] or "Texas lip fern".[1][4][3]
Further molecular studies in Myriopteris demonstrated the existence of three well-supported clades within the genus. M. allosuroides belongs to what Grusz et al. informally named the alabamensis clade, and is sister to a group consisting of M. microphylla, M. moritziana, M. scabra, and M. fimbriata.[10]
Distribution and habitat
Myriopteris aemula is found in scattered locations in southern Texas, including the Trans-Pecos.[4][11] Its range extends throughout the length of Mexico, particularly in the eastern and central states, as far south as Chiapas.[2]
The species grows on limestone bedrock, on rocky slopes and ledges,[1][4][2] and in cracks and openings in the rock.[3] It occurs at an altitude from 100 to 1,800 meters (330 to 5,900 ft).[1][2]
Ecology and conservation
While globally secure (G4), M. aemula is considered by NatureServe to be vulnerable in Texas.[12]
Citations
- Windham & Rabe 1993.
- Mickel & Smith 2004, p. 180.
- Lellinger 1985, p. 139.
- Diggs & Lipscomb 2014, p. 232.
- Diggs & Lipscomb 2014, p. 231.
- Maxon 1908, p. 495.
- Grusz & Windham 2013.
- Christenhusz, Fay & Byng, p. 9.
- Diggs & Lipscomb 2014, p. 230.
- Grusz et al. 2014, p. 704.
- Kartesz 2014.
- NatureServe 2018.
References
- Christenhusz, Maarten J. M.; Fay, Michael F.; Byng, James W. Plant Gateway's the Global Flora: A practical flora to vascular plant species of the world. 4. ISBN 978-0-9929993-9-1.
- Diggs, George M., Jr.; Lipscomb, Barney L. (2014). The Ferns and Lycophytes of Texas. Fort Worth, Texas: Botanical Research Institute of Texas Press. ISBN 978-1-889878-37-9.
- Grusz, Amanda L.; Windham, Michael D. (2013). "Toward a monophyletic Cheilanthes: The resurrection and recircumscription of Myriopteris (Pteridaceae)". PhytoKeys. 32: 49–64. doi:10.3897/phytokeys.32.6733. PMC 3881352. PMID 24399906.
- Grusz, Amanda L.; Windham, Michael D.; Yatskievych, George; Huiet, Lane; Gastony, Gerald J.; Pryer, Kathleen M. (2014). "Patterns of Diversification in the Xeric-adapted Fern Genus Myriopteris (Pteridaceae)". Systematic Botany. 39 (3): 698–714. doi:10.1600/036364414X681518. JSTOR 24546228. PMC 4651630. PMID 26649266.
- Kartesz, John T. (2014). "Myriopteris". Biota of North America Program.
- Lellinger, David B. (1985). A Field Manual of the Ferns & Fern-Allies of the United States & Canada. Washington, DC: Smithsonian Institution Press. ISBN 0-87474-603-5.
- Maxon, William R. (1908). "Studies of Tropical American Ferns-No. 1". Contributions from the United States National Herbarium. 10 (7).
- Mickel, John T.; Smith, Alan R. (2004). The Pteridophytes of Mexico. Memoirs of the New York Botanical Garden. 88. Bronx, New York: New York Botanical Garden. ISBN 978-0-89327-488-7.
- "Cheilanthes aemula". NatureServe. March 2018. Retrieved January 30, 2019.
- Windham, Michael D.; Rabe, Eric W. (1993). "Cheilanthes aemula". In Flora of North America Editorial Committee (ed.). Flora of North America North of Mexico. 2: Pteridophytes and Gymnosperms. New York and Oxford: Oxford University Press. Retrieved January 30, 2019.