Pteridium caudatum

Schwartsburd, Pedro B., Navarrete, Hugo, Smith, Alan R. & Kessler, Michael, 2017, Prodromus of a fern flora for Bolivia. XXVI. Dennstaedtiaceae, Phytotaxa 332 (3), pp. 251-268 : 263

Pteridium caudatum (L.) Maxon, Proc. U.S. Natl. Mus. 23: 631. 1901.

= Pteridium aquilinum var. caudatum (L.) Christ, Jahrb. Hamburg. Wiss. Anst. Beih. 14(Beih. 3): 5. 1896.

= Pteridium aquilinum subsp. caudatum (L.) Bonap., Notes Ptéridol. 1: 62. 1915.

Range:— Antilles; mountains from central Mexico to Venezuela and Bolivia (LP, SC).

Ecology:— Locally fairly common; terrestrial, often scandent, weedy in cultivated areas, fallows, roadsides; less common, shorter-lived, and less aggressive than P. esculentum ; to 2300 m.

Notes:— Pteridium caudatum is thought to be, at least in part, a fertile hybrid of allopolyploid origin between elements within P. aquilinum and South American P. esculentum . Thomson & Alonso-Amelot (2002) postulated that the “heterogeneity observed within P. caudatum is consistent with multiple origins through independent hybridization events”, and presented the case for past hybridization between the southern hemisphere diploid P. arachnoideum (here treated as P. esculentum subsp. arachnoideum ), and various northern hemisphere diploids, including the North American P. aquilinum subsp. pubescens (Underw.) Piper & Beattie and P. aquilinum var. pseudocaudatum (Clute) Domin (see also discussion by Hieronymus 1909, Mickel & Beitel 1988). These multiple origins have created a number of different morphotypes. There is also the possibility of backcrosses and polyploidization between various morphotypes of P. caudatum , and in fact diploids, tetraploids, and perhaps hexaploids are all known ( Wolf et al. 2015). The totality of evidence suggests that there has been genetic isolation of taxa with historically overlapping distributions, and the morphological, biochemical, and ecological data all validate recognition of P. caudatum , a composite taxon, at species rank. This hybridogenic origin of P. caudatum was reaffirmed by Wolf et al. (2015): “We also posit that P. caudatum may include recent diploid hybrids, backcrosses to P. esculentum , as well as allotetraploid plants”. In this treatment for Bolivia we apply the name P. caudatum in a broad morphological sense, and acknowledge that the taxon so treated may have had multiple independent origins.

Besides the characters shown in the key, Pteridium caudatum differs from subspecies of P. esculentum by smaller blade sizes and more thin-textured, finely divided blades. Presumed juvenile plants from Amazonia look strikingly different from adult plants in having more finely dissected blades with smaller ultimate blade divisions; they may be mistaken for Dennstaedtia .