The discovery of Adoketophyton subverticillatum from the Devonian Mangshan Group of Duyun, Guizhou Province and its significance
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Abstract:
Adoketophyton subverticillatum (Li et Cai) Li et Edwards is one of the representative and well-known plants in the Early Devonian Posongchong flora of Yunnan, and its external morphology and anatomy have been described in detail. One specimen collected from the lower part of the Mangshan Group at the Baoyang section of Duyun, Guizhou Province is assigned herein to A. subverticillatum, based on features revealed by serial dégagement. The specimen, broken at both ends, is ca. 19.3 mm long, and shows a fertile axis comprising of sporophylls and sporangia. The fertile axis is slender, ca. 0.9 mm wide. The fan-shaped sporophylls, 6.2 mm in length and 6.4 mm in maximum width when complete, are oppositely and decussately inserted on the fertile axis to form four vertical rows. An incomplete sporangium reaches up to 4.1 mm high and 1.1 mm wide. The temporal and spatial distribution of Adoketophyton indicates that this genus is a representative element of the Early Devonian floras, thus suggesting an Early Devonian age for the lower part of the Mangshan Group. The discovery of A. subverticillatum in Duyun confirms the dispersal and interrelationship at the genus and species levels between the Posongchong flora of Yunnan and plants from the Mangshan Group of Duyun, Guizhou. The studies of Adoketophyton and other related taxa suggest that leafy structures, such as sporophylls, bracts, and branch-leaf complexes, were widespread in the South China Block during the Early Devonian, when the atmospheric CO2 level was high.
