Abstract
Podocarpium A. Braun ex Stizenberger is one of the most common legumes in the Neogene of Eurasia, including fossil fruits, seeds, leaves, and possible flower and pollen grains. This genus is not completely consistent with any extant genera according to gross morphological characters and poorly preserved cuticular structures reported in previous studies. The fossil pods collected from the coal-bearing series of the Changchang Basin of Hainan Island and Maoming Basin of Guangdong, South China, are examined by morphologically comparative work, with special reference to venation patterns and placental position. These distinctive features, as well as the ovule development of pods from different developmental stages and the epidermal structure of the pods, as distinguished from previous records lead to the conclusion that these fossils can be recognized as a new species of Podocarpium, P. eocenicum sp. nov. This new discovery indicates that Podocarpium had arrived in South China by the Eocene. Investigation on the fossil records of this extinct genus shows that P. eocenicum is the earliest and lowest latitude fossil data. The possible occurrence pattern of this genus is revealed as follows: Podocarpium had distributed in the South China at least in the middle Eocene, and then migrated to Europe during the Oligocene; in the Miocene this genus reached its peak in Eurasia, spreading extensively across subtropical areas to warm temperate areas; finally, Podocarpium shrank rapidly and became extinct in Eurasia during the Pliocene.
Highlights
IntroductionThis treatment was held by Herendeen (1992a,b) alike, and he proposed a new combination to replace the illegitimate name Podogonium knorrii Heer which is universally known
Heer’s taxonomic treatment was poorly accepted because: (1) considerable continuous morphological variation occurs to the fossil leaflets; (2) the Eocene Podocarpium from South China fruits of Heer’s original six species can not be distinguished morphologically (Kirchheimer, 1957; Herendeen, 1992a)
It was once thought that legumes probably evolved in the humid tropics in the late Cretaceous (Sprent, 2007), and the remains of this age have been reported from many localities, such as the Caucasus, Sudan, Somalia and Mexico, and Siberia, Cananda, and Colombia, Central India, and China (Raven and Polhill, 1981; Muller, 1984; Giraud and Lejal-Nicol, 1989; Awasthi, 1992; Guo and Zhou, 1992; Herendeen et al, 1992; Shakryl, 1992; Wang et al, 2007)
Summary
This treatment was held by Herendeen (1992a,b) alike, and he proposed a new combination to replace the illegitimate name Podogonium knorrii Heer which is universally known. The pod of Podocarpium, which has very distinctive features, such as generally tardy dehiscence, elliptical shaped, single-seeded and having a long stipe, was originally illustrated as an unidentified fruit by Knorr (1755), and almost a century it was considered to be related to this genus (Braun, 1845; Herendeen, 1992b). Podocarpium has been extensively reported in many fossil floras of Eurasia from the early Oligocene to the Pliocene (Liu et al, 2001b; Wang et al, 2007)
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