Monographs Details: Pteridium arachnoideum (Kaulf.) Maxon
Authority: Mickel, John T. & Smith, Alan R. 2004. The pteridophytes of Mexico. Mem. New York Bot. Gard. 88: 1-1054.
Family:Dennstaedtiaceae
Description:Species Description - Fronds (1–)1.5–3 m long; blades with free lobes or rarely long decurrent segment bases between ultimate segments; rachises glabrous to slightly pubescent; penultimate axes pubescent abaxially with hairs scattered to dense, curly, clear, 0.5 mm, with dark end walls, adaxially with hairs white, especially in medial grooves; costae and veins usually sulcate abaxially; laminar surfaces densely hairy abaxially on veins with hairs 0.5–0.8 mm, twisted, white, and hairs minute, arachnoid, white, covering the laminar surfaces between veins, adaxially with scattered, white hairs mostly along margins, minute glandular hairs absent; false indusia 0.1– 0.3 mm wide with erose margins with rare to scattered cilia; 2n=104 (Trin), 208 (Galapagos).

Discussion:

Pteris arachnoidea Kaulf., Enum. Filic. 190. 1824. Pteris aquilina L. var. arachnoidea (Kaulf.) D. C. Eaton, Proc. Amer. Acad. Arts, ser. 2, 8: 203. 1861. Pteridium aquilinum (L.) Kuhn var. arachnoideum (Kaulf.) Brade, Z. Deutsch. Ver. Wiss. Kunst. Sa˜o Paulo 1: 56. 1920. Pteridium caudatum (L.) Maxon subsp. arachnoideum (Kaulf.) Lellinger, Amer. Fern J. 93: 150. 2003. Type. Brazil. Chamisso s.n. (LE!, photo GH). For additional synonymy, see R. Tryon (1941).

Unverified, Doubtful, or Mistaken Reports. Mor (reported by Riba et al., 1996, but cited specimens misidentified, or doubtful). Tab (reported by Magan˜a, 1992, but figured plant is P. caudatum). Pteridium arachnoideum is distinguished most readily by free lobes between the segments near the tips of the pinnae.