Christella H.Lév., Fl. Kouy-Tchéou

Smith, Alan R. & Kessler, Michael, 2017, Prodromus of a fern flora for Bolivia. XXX. Thelypteridaceae, Phytotaxa 331 (1), pp. 1-34 : 19

Christella H.Lév., Fl. Kouy-Tchéou 472. 1915.

This genus, with about 20 species in the neotropics and perhaps 50 in the paleotropics, is characterized by 1-pinnate-pinnatifid blades with or without gradually reduced proximal pinnae, veins united below the sinuses or connivent at the sinuses, lack of the cartilaginous keel as in Steiropteris , persistent indusia, lack of aerophores at the pinna bases, and chromosome base number x = 36. As circumscribed here, Christella excludes Amblovenatum and Cyclosorus , the former an introduced, widely naturalized genus in Bolivia, the latter pantropical, with only two species. Some species of Christella are common and often weedy along roadsides and in ditches.

Available information suggests that Christella , as here construed, is not monophyletic ( He & Zhang 2012, Almeida et al. 2016) and that many (but not all) of the neotropical species are not closely allied to those in southeast Asia (type locality). Holttum (1974) adopted a new sectional name, Christella sect. Pelazoneuron , for nine species in Africa and Madagascar characterized by having veins from adjacent segments running to, or anastomosing at, sinuses; curiously, he chose a neotropical species, Christella patens , as type, without alluding to the existence of any other New World species. Only two neotropical species have this far been sequenced, neither of which occurs in Bolivia. Given the uncertainty as to how broadly to apply Christella , the inadequate sampling of related groups in the Old World, and the lack of evidence for most New World species in this group ( Thelypteris sect. Cyclosorus of Smith 1971), it seems expedient to accept the Holttum classification for now, tentative though it may be.

Useful characters for distinguishing species of Christella include: rhizome habit (creeping or erect, apex hidden by old leaf bases); proximal pinnae reduced or not, auriculate at acroscopic bases or not; venation (lowermost veins from adjacent segments united at an obtuse angle below sinuses and producing an excurrent vein vs. veins connivent at or meeting margin at sinuses); pubescence (hair length, density, and location) and scales (present or absent) on blades and costae abaxially. Polyploidy is well known among the neotropical species ( Smith 1971).

We include also Cyclosorus s.s. and Amblovenatum in the key, as they are also often confused with, accepted as, and/or possibly related to, elements within Christella s.l..