J Syst Evol ›› 1983, Vol. 21 ›› Issue (2): 153-160.

• Research Articles • Previous Articles     Next Articles

Palaeosmunda Emended and Two New Species

Li Zhong-Ming   

  1. (Institute of Natural History, Beijing Natural History Museun)
  • Online:1983-05-18 Published:1983-05-18

Abstract: The genus Palaeosmunda was established by R. E. Gould in 1970 based upon some Late Permian Osmundaceous trunks with well-developed leaf gaps and rhomboidal sclerotic ring within petiolar base seen in cross section. As he thinks that the latter character is more important than the former, this genus could not be assigned to any subfamily of Osmundaceae. However, the leaf gap is one of the most important characters in the structure of the fern stem, so the author suggests that this genus should be assigned to subfamily Osmundoideae and its diagnosis must be emended as follows: The genus Palaeosmunda is represented by some rhizomes (or trunks), roots and leaf bases of ferns which structurally are preserved, resembling Osmundacaulis but which can’t be assigned to any group of this genus. Stem containing an ectophloic dictyoxylic siphonostele; if tracheids present in the pith, they being multiseriate scalariform pitted; pith or cortex sometimes contain ing groups of secretory cells or sclerenchyma; number of leaf traces seen in a tran sverse section of cortex more than 30; leaf traces adaxially curvature, rarely oblong shaped; petiolar bases with or without stipular expansion, containing a C-shaped vascular strand; root diarch. Type species——Palaeosmunda williamsii. According to this diagnosis some primitive osmundaceous species with the leaf gaps, which have already found in Upper Permian and Lower Triassic, could be assigned to this genus. Two of them are P. williamsii Gould and P. playfordii Gould, and Osmundacaulis beardmorensis, which was from Lower Triassic of Antarctica in 1978, should be assigned to the genus Palaeosmunda. In this paper two osmundaceous new species: P. primitiva and P. plenasioides were found in the coal balls of Upper Permian age from Wangjiazhai of Shuicheng of Guizhou Province, China. P. primitiva is represented by two trunks; stem about 4 cm in diameter; stele actophloic dictyoxylic siphonostele; pith cavity about 3—4 mm in diameter, contianing parenchyma and tracheids; xylem cylinder thin, less than 10 tracheids in radial thickness, dissected by leaf gaps. Inner cortex about 1.5 cm thick, mainly parenchymatous, but sometimes containing a few sclerenchymatous; number of leaf traces seen in a transverse section about 50—60; leaf traces departing at 35—45º,open C-shaped at point of departure, gradually becoming shallow C-shaped or V-shaped in different parts; protoxylem in base of leaf traces single, endarch; when leaf traces pass through inner cortex, protoxylem biturcating. Petiole bases without stipular expansion, probablyloosely embracing the stem; xylem strand of potiole trace shallow C-shaped, surrounded by selerenchyma; sclerotic ring round, connected with single sclerenchyma mass in the concavity of the petiole trace. Root arising singly from leaf trace, diarch, with inner and outer cortex. P. plenasioides is represented by a rhizome; stem more than 4 cm in diameter; stele actophloic dictyoxylic siphonostele; xylem cylider with about 20 tracheids in radial thickness, dissected by leaf gaps; xylem bundle U-, O-, or crosier- (i.e. query-) shaped; pith and inner cortex parenchymatous, with many groups of secretory cells; leaf trace C-shaped, its base containing two endarch protoxylem groups; root diareh,with inner and outer cortex, arising singly from leaf trace or its base.

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