J Integr Plant Biol. ›› 1966, Vol. 14 ›› Issue (1): -.

• Research Articles •    

On Plant-Remains from the Devonian of Yunnan and their Significance in the Identification of the Stratigraphical Sequence of this Region

Hsü Jen(J. Hsü)   

Abstract: The present paper treats of three plant-remains recently collected in the district Chu-tsing, East Yunnan. They are Zosterophyllum yunnanicum sp. nov., Protopteridium minuturn Halle and Sporogonites yunnanense sp. nov., and their distinctions from the related species from the other parts of the world are rather fully discussed. In addition, the paper further discusses the geological age of the region wherefrom these and other plant-remains have been collected. Zosterophyllum yunnanicum is preserved in a bed of dark greyish sandy clay in the locality Hsu-Chia-Chong in the district Chuitsing, East Yunnan. It is associated with Drepanophycus spinaeformis Goeppert. This bed belongs to the uppermost layer of the Tsuifengshan Series. The diagnosis of Zosterophyllum yunnanicumsp, nov. is given as follows: A small plant with slender erect axes, about 1-1.3 mm across and sparingly dicho- tomous branches, axis possessing a slender central vascular strand. Sporangia are short-stalked, closely and radially arranged on the upper part of the erect axis to form a compact strobilus, up to 5 cm long. Each strobilus consists of about 40–50 sporangia which are roundish to reniform, about 1.9–2.7 mm across, and about 9.4 mm thick; dehiscence by a slit running along the convex upper edge. Epidermal cells of the axis and the sporangium are elongate-fusiform, about 360 μ long and 45-90μ wide. Zosterophyllum yunnanicum agrees with Z. myretonianum Penh. and Z. australianum in general morphology, but smaller in size. The genus Zosterophyllum has so far been recorded only from the Late Silurian of Australia and England and the Early Devonian of England, Scotland, France, Germany, West Siberia and North America. Remains of axes with H-shaped branching (cf. Zostero- phyllum) have previously been recorded by the present author from the district Chutsing (Hsu 1947, 354-355. Pl. V, Fig. 52 and text-figs. 5 a-c), but the actual locality and horizon were then unknown. So the present discovery of Z. yunnanicum helps to settle the question of the Tsuifengshan Series which is definitely not younger than the Late Devonian in age. Protopteridium minutum and Sporogonites yunnanense were found in a bed of light grey sandstone in the locality Lunghuashan of the same district, from where the type of Protopteridium minutum Halle was collected. From the same bed some fragments of Protolepidodendron scharyanum Krejci were observed. This bed belongs to the uppermost layer of the Lunghuashan Series. From the lower part of the same series fragments of Drepanophycus spinaeformis Goeppert were also collected. It is interesting to note that under a critical investigation by the present author, it conclusively proves that Proto-pteridium minutum is not a small plant, as Halle first described. It attains a height of at least 1 meter. The main axis measures about 1.8 cm in diameter. Both the larger and the smaller specimens show sympodial development. Unequally dichotomous branching has been found only in some primary and secondary lateral branches. Most of the lateral branches are pinnulelike and subdivide 4–6 times, each possessing a slender central vascular strand. If the terminology of Zimmermann is adopted, the type of branching may be described as "Oscillating overtopping". However, some slender branches have been observed. These branches are sparingly unequally dichotomous, forking 6–7 times, and appear to be thinner than those just mentioned. Young branches are circinately coiled. Sporangia are arranged in clusters, 2-4-8 in number, attached to the terminal branches. These sporangia are 0.9 mm long, fusiform or sometimes almost cylindrical. Some larger obovate ones are about 2.5 mm long and borne singly, or in 2 (rarely in 4) in each tassel on the top of the flattened lateral branches. Epidermal cells of the axes are elongate, about 136 Ft long and 45.5 μ wide, while those of the smaller sporangia are oblong-fusiform, about 100–150 μ long and 25 μ wide and those of the larger, about 130–230μ long and 40–70μ wide. No annulus is observed. Sometimes mineral grains, occupying the interior of the sporangia, are observable through a longitudinal slit in the wall and thus give false markings of cells. Evidently, the plant-body of Protopteridium minutum is much more complex than Halle thought. A new reconstruction of it is drawn here to replace that given by Halle in 1936. It is considered that Protopteridium minutum is more closely related to P. hostimense Krejci than to others. The former is also complex in the vegetative branches, but simpler in the fertile ones. Sporogonites yunnanense is represented only by some detached capsules, hich are elongate-obovate, measuring about 3.2–4.5 mm long and 1.4–1.8 mm wide. These capsules are borne on the top of a slender stalk, measuring about 0.4–0.8 mm across. The younger ones look rather smooth, but the mature ones exhibit 12 longitudinal ridges, separated by shallow grooves, 6 ridges being visible on the surface exposed. Epidermal cells of the wall of the capsules are elongate, 150μ long and 50 μ wide. No stomata could be made out among them. Sporogonites yunnanense closely resembles S. exaberans Halle of the Early Devonian, but the capsules of the former exhibit variable forms and the upper end of the capsules is rather more pointed than those of the latter. Owing to the occurrence of Drepanophycus spinaeformis and the general aspect of the flora so far known, the author suggests that the geological age of the Lunghuashan Series is of the Middle Devonian or probably the Early Eifelian. The flora of the Tsuifengshan Series is predominated by Drepanophycus spinaeformis and Zosterophyllum yunnanicum, thus indicating that its geological age is no doubt of the Early Devonian.

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