Frond reconstruction of Pecopteris lativenosa Halle emend. Li et al.
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Abstract:
Pecopteris lativenosa Halle emend. Li et al. has been widely reported from the upper Paleozoic of North China. However, all previously reported specimens are incomplete with great morphological variation, leading to frustration in their identifications. In recent years, an autochthonous early Permian swamp forest, the Wuda Tuff flora, has been discovered from the volcanic tuff layer between coal No. 6 and coal No. 7 in Wuda Coalfield, Inner Mongolia. This flora has yielded large, relatively complete specimens with fine anatomical details, enabling an in-depth evaluation of intraspecific morphological variation of Pecopteris lativenosa. In this report, the ultimate pinnae of Pecopteris lativenosa are divided into four types: UP3, UP7, UP2, and UP1; penultimate pinnae are divided into six types: PP1, PP2, PP3, PP4, PP5, and PP6. On a penultimate rachis, ultimate pinnae vary from apex to base in a sequence of undivided, pinnatifid, pinnatipartite and pinnatisect types, with UP3, UP7, and UP2 all located on the apical part of the penultimate pinna. Penultimate pinnae on an antepenultimate rachis also vary from apex to base in a sequence of undivided, pinnatifid, pinnatipartite and pinnatisect types, with PP6, PP5, PP4, PP3, and PP2 all located on the apical part of the antepenultimate pinna. On an antepenultimate pinna, the basal penultimate pinnae are about 20 cm long, shorter than those penultimate pinnae in the middle, which are about 47 cm long. A pair of aphlebiae are attached at the base of the antepenultimate rachis. Based upon these observations, an entire tripinnate frond of Pecopteris lativenosa is reconstructed. In addition, the leaf scars are arranged in two longitudinal rows, showing the Caulopteris obovatus type. The type specimens described by Halle in 1927 likely represent penultimate pinna types PP2 and PP3 from the distal parts of antepenultimate pinnae.
