Pteridium arachnoideum (Kaulf.) Maxon

  • Authority

    Mickel, John T. & Beitel, Joseph M. 1988. Pteridophyte Flora of Oaxaca, Mexico. Mem. New York Bot. Gard. 46: 1-580.

  • Family

    Dennstaedtiaceae

  • Scientific Name

    Pteridium arachnoideum (Kaulf.) Maxon

  • Description

    Species Description - Fronds (1-) 1.5-3 m long, with free lobes or long-decurrent segment bases between segments; rachis glabrous to slightly pubescent; penultimate axes pubescent abaxially with hairs scattered to dense, curly, clear, 0.5 mm, with brown septa, adaxially with hairs white, especially in medial groove; midveins and veins usually sulcate; laminar surface densely hairy with 0.5-0.8 mm hairs twisted, white, on veins and hairs minute, arachnoid, white, covering the laminar surface between veins, adaxially with hairs scattered, white, mostly along margin; false indusium 0.1-0.3 mm wide with erose margin with rare to scattered cilia.

  • Discussion

    Pteris arachnoidea Kaulfuss, Enum. filic. 190. 1824. Pteris aquilina Linnaeus var. arachnoidea (Kaulfuss) D. C. Eaton, Proc. Amer. Acad. Arts II, 8: 203. 1861. Pteridium aquilinum (Linnaeus) Kuhn var. arachnoideum (Kaulfuss) Brade, Z. Deutsch. Ver. Wiss. Kunst. São Paulo 1: 56. 1920. Type. Brazil. Chamisso s.n. (LE!, photo GH). For additional synonymy, see R. Tryon (1941). Pteridium arachnoideum is distinguished by possession of the full suite of characters as given in the key and description (free lobes, minute arachnoid hairs, narrow ciliate indusia, no glandular hairs, twisted clear hairs with dark end walls). Intermediate specimens with these characters and the characters of one of the other taxa exhibited some degree of frond irregularity and probably represent hybrid individuals. The combination P. arachnoideum x caudatum has the narrow, ciliate margin and arachnoid hairs of P. arachnoideum coupled with the glandular adaxial hairs and clavate abaxial hairs of P. caudatum. Specimens exhibiting this combination of characters are: 5854 (Tuxtepec, 250-650 m), 6433 and 6434 (Ixtlán, 450-600 m), 6666 (Tuxtepec, 550 m), 7366 (Tuxtepec, 300 m), and Hallberg 1755 (Tehuantepec, 650-900 m, NY). The combination Pteridium arachnoideum x feei has the arachnoid hairs of P. arachnoideum coupled with the long (1-1.5 mm), straight brown hairs of P. feei. The plants are found at higher elevation and the ciliate indusia are narrow to broad: 910 (Villa Alta, 2050-2200 m) and 4458 (Ixtlán, 1900 m). For the combination P. caudatum x feei (lacking arachnoid hairs), see the discussion under P. caudatum.

  • Distribution

    Open, disturbed areas; Ixtlán, Juchitán, Mixe, Teotitlán, Villa Alta; 100-2450 m. Mexico (Gro, Mex, Hgo, Ver, Pue, Oax, Chis); Guat to Pan; Gr An till, St. Lucia, Trin; Col to Fr Gui, to Braz & n Arg.

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