Tree ferns in ferment

The scaly tree ferns (Cyatheaceae) have been the subject of numerous publications and remodeling lately. In an effort to curate and update our collections, and particularly the specimen scan database, I put together this bibliography and primer on the shifting outlines of genera, and in some cases, species, of Cyatheaceae. This was for my own use, as a non-fern-specialist, in curating the collection -  but my time was limited, so caveat emptor! And carpe filicum.

Of the roughly 600 species of Cyatheaceae, about 200 are Neotropical, the majority belonging to the genus Cyathea (Lehnert  2009). They are especially species-rich on the eastern slope of the Andes, and into the mountains of Central America. They also occur in the Antilles, in the Guiana highlands of northern South America, and in the Mata Atlantica of southeastern Brazil. The most recent molecular studies by Korall et al. (2006, 2007), support recognition of the genera Sphaeropteris s.s., Alsophila, Gymnosphaera, and Cyathea.  These are also accepted at the genus level in the most recent classification of ferns. (Smith et al. 2006)

The genus Sphaeropteris is mostly paleotropical. Tryon (1970) had recognized about 20 neotropical species, but by his own admission (Tryon 1971), only about six of these were clearly allied to the paleotropical species. The remainder, which had been placed in subg. Sclephropteris by Windisch in 1977, were moved by Lellinger (1987) back into Cyathea, and this is supported by molecular studies. The six neotropical species remaining in Sphaeropteris (termed the "Sphaeropteris horrida group" by Tryon 1971) are: S. insignis, S. horrida, S. brunei, S. cuatrecasasii, S. quindiuensis, & S. gardneri.

Alsophila has about 30 neotropical and 200 paleotropical species (Conant 1983), including species previously placed in Nephelea (monographed by Gastony 1973). About half of the species of Alsophila in the neotropics are endemic to the Antilles.

Gymnosphaera has often been treated as a group or section within Alsophila (e.g. Holttum & Edwards 1983). Up until 2007, Alsophila salvinii had been treated as the only neotropical species of the Gymnosphaera group (Holttum & Edwards 1983), but Korall et al. (2007), found A. capensis to be included here as well. The specimen of A. capensis sampled by Korall is probably paleotropical. However, Alsophila capensis ssp. polypodioides is known from southern Brazil.  These two neotropical taxa have not yet been transferred to Gymnosphaera but likely will be in the near future.

The genus Cyathea in its current circumscription has roughly 160-170 neotropical species. An additional 8 paleotropical (Western Pacific) species comprise the 'Cyathea decurrens group.' Cyathea is now considered to include Cnemidaria, Trichipteris, Sphaeropteris subg. Sclephropteris, and probably Hymenophyllopsis.

Trichipteris (ca 55 species) was defined by Tryon (1970) and Tryon & Stolze (1989) by its lack of indusia, but this was considered by Lellinger (1987) to be an artificial character. He, among others, interpreted Trichipteris as an unnatural group of species, better placed in Cyathea, and this is supported by molecular studies.

Cnemidaria (ca 25 species) was long considered a distinct natural group, and may indeed form a monophyletic clade  though further sampling is needed to justify its recognition as a distinct subgenus (Lehnert 2012). The discovery through DNA analysis that it nests within Cyathea was somewhat of a surprise. It is generally distinguished by its lack of a tree-like trunk, its leaves often simple-pinnate to pinnatifid (vs. bi- to tri-pinnate), a characteristic venation pattern, and its smooth spores. The most recent monograph of this group was provided by now-retired Field Museum curator Bob Stolze (1974). Lehnert (2012) provides names in Cyathea for the Cnemidaria species which needed them.

The inclusion of Hymenophyllopsis within Cyathea was even more surprising. These six diminutive species endemic to the region of the Venezuelan tepuis resemble filmy ferns, with thin, lacy leaves only ca 3-4 cell layers thick, and pouch-shaped indusia, and were long placed in their own family. Only in 1999 did a molecular analysis show their real affinities to the Cyatheaceae. Smith et al. (2006) maintain Hymenophyllopsis as separate, presumably on the grounds of its distinct morphology, and still imprecise placement relative to other species. Korall et al. (2007) found the paleotropical Cyathea decurrens group to be sister to the neotropical Cyathea. The single species of Hymenophyllopsis sampled appears as 'sister' to the rest of neotropical Cyathea; however this exact placement is still preliminary ("not well supported"), and more data are needed. Christenhusz (2009) treats it as a subgenus of Cyathea, and published the required new names.

Marcus Lehnert, of Stuttgart (STU), following much fieldwork and observation of living plants, has recently published several preliminary partial treatments, regional checklists, and new species of Cyathea. Lehnert (2008) notes that Cyathea pallescens, as treated by earlier authors was based on confusion about which specimen was the type. The true C. pallescens is limited to northern Ecuador (Carchi, Pichincha) and Nariño, Colombia, and C. halonata Moran is a synonym. The correct name for C. pallescens sensu Tryon is C. tungurahuae. Lehnert also describes or rescues from synonymy several new species in the C. pallescens complex. Lehnert (2009) similarly redivides and remodels the species complex surrounding Cyathea caracasana, recognizing C. caracasana sensu strictu only from the Antilles, Colombia and northern Venezuela. In all 12 species synonymized by Tryon with C. caracasana are recognized as distinct by Lehnert. Tryon's var. chimborazensis is found to be more closely related to the "C. pallescens group." Other previously recognized varieties (e.g. var. meridensis and var. maxonii) are elevated to species status. Variety boliviensis at species level becomes a synonym of C. squamipes. Cyathea herzogii, previously treated mistakenly as a synonym of var. boliviensis, is recognized as a valid species, until now commonly submerged into the widespread C. delgadii. And this is just a sampling of the convulsive change in Cyathea! Meanwhile, Lehnert (2011A) provides a key to what he considers to be rough natural groupings in Cyathea, briefly inventories the paleotropical Cyathea decurrens group, and provides a synopsis of four informal species-groups of neotropical Cyathea which show affinities to the Cyathea decurrens group. This is important to future phylogenetic studies in that this group is the sister-group to all neotropical members of Cyathea. Lehnert (2012) provides a synopsis of the species previously placed in Cnemidaria, together with other species of similar morphology (pinnate to pinnate-pinnatifid fronds.)
    The taxonomic upheavals are too many to summarize here, and there are surely more to come -- a bibliography of Lehnert's publications and other publications of historical importance is provided below.

    Our online specimen collection had originally recognized Trichipteris and Cnemidaria, following the Flora of Peru treatment, but is now updated to place these genera in Cyathea. Names are curated as possible in accordance with publications by Lehnert & Christenhusz, though individual plant ID's are not all confirmed. 
    Prior to this curation, we had 54 species and 109 specimen scans of Cyatheaceae, and within the following several months, we will triple the species number to 154 species and quadruple the number of scans to 419. They're in the scanning queue now!

    Many thanks to Blanca León (USM / TEX), our former Field Museum colleague for recently bringing Lehnert's publications to our attention. Blanca has provided us with many collections, identifications and curatorial expertise over the years, and generously selected and organized our original fern reference collection.

(not complete - several recent new species papers, notably by eminent Drs. A.Rojas, B.León, R.Moran, and Allan Smith are omitted - for time constraints only!)

Barrington, D.S. 1978. A revision of the genus Trichipteris. Contr. Gray Herb. 208: 3-93. [available on BHL]

Christenhusz, M. 2009. New combinations and an overview of Cyathea subg. Hymenophyllopsis (Cyatheaceae). Phytotaxa 1: 37-42.

Conant, D.S. 1983. A revision of the genus Alsophila (Cyatheaceae) in the Americas. J. Arnold Arbor. 64: 333-382. [available on BHL; includes transfers for species of Nephelea treated by Gastony.]

Gastony,G. 1973. A revision of the fern genus Nephelea Contr. Gray Herb. 203: 81-148. [available in BHL]

Holttum, R.E. & P. J. Edwards, 1983. The tree-ferns of Mount Roraima and neighbouring areas of the Guayana Highlands with comments on the family Cyatheaceae. Kew Bull. 38: 155-188.

Lehnert, M. 2003. Six new species of tree ferns from the Andes. Amer. Fern Journ. 93(4): 169-183.

Lehnert, M. 2006. The Cyatheaceae and Dicksoniaceae (Pteridophyta) of Bolivia. Brittonia 58(3): 229-244.

Lehnert, M. 2006A. New species and records of tree ferns (Cyatheaceae, Pteridophyta) from the Northern Andes. Org. Divers. Evol. 6, Electr. Suppl. 13: 1-11.

Lehnert, M. 2006B. Two new tree ferns (Cyatheaceae) from southern Ecuador. Brittonia 58: 4-9.

Lehnert, M. 2008. On the identification of Cyathea pallescens (Sodiro) Domin (Cyatheaceae): typifications, reinstatements and new descriptions of common Neotropical tree ferns. Bot. Journ. Linn. Soc. 158: 621-649.

Lehnert, M. 2009. Resolving the Cyathea caracasana complex (Polypodiopsida: Cyatheaceae). Stuttg. Beitr. Naturk. A, N.S. 2: 409-445.

Lehnert, M. 2009A. Three new species of scaly tree ferns (Cyathea-Cyatheaceae) from the northern Andes. Phytotaxa 1: 43-56.

Lehnert, M. 2011. The Cyatheaceae (Polypodiopsida) of Peru. Brittonia 63(1): 11-45.

Lehnert, M. 2011A. Species of Cyathea in America related to the western Pacific species C. decurrens. Phytotaxa 26: 39-59. [Synopsis of 8 paleotropical and 32 neotropical species.]

Lehnert, M. 2012. A synopsis of the species of Cyathea (Cyatheaceae-Polypodiopsida) with pinnate to pinnate-pinnatifid fronds. Phytotaxa 61: 17-36. [Keys and synopsis of 57 species and 8 varieties; many new combinations and names based on former Cnemidaria spp.]

Lehnert, M. 2014. Do you know Cyathea divergens (Cyatheaceae-Polypodiopsida)? Phytotaxa 161: 1-42. [Added Feb 2014; not represented in above discussion.]

Lellinger,D. 1987. The disposition of Trichopteris (Cyatheaceae). Amer. Fern. J. 77: 90-94.

Murillo-A, J. & M.T. Murillo. 2003. Pteridófitos de Colombia IV. Novedades in Cyathea (Cyatheaceae). Rev. Acad. Colomb. Cienc. 27(102): 45-51. [open access] [Includes checklist of Colombian species, 55 spp and 5 var's. Cnemidaria spp not included.]

Smith,A.R. et al. 2006. A classification for extant ferns. Taxon 55(3): 705-731. [Open Access]

Stolze, R. 1974. A taxonomic revision of the genus Cnemidaria (Cyatheaceae). Fieldiana, Bot. 37: 1-98.

Tryon, R.M. 1970. The classification of the Cyatheaceae. Contr. Gray Herb. 200: 3-50.

Tryon, R.M. 1971. The American tree ferns allied to Sphaeropteris horrida. Rhodora 73: 1-19. [available on BHL]

Tryon, R.M. 1976. A revision of the genus Cyathea. Contr. Gray Herb. 206: 19-98.

Tryon, R.M. & R. G. Stolze. 1989. Pteridophyta of Peru. Part I. 1. Ophioglossaceae-12. Cyatheaceae. Fieldiana Bot., n.s. 20: 1-145.