A new species of Lepidostrobus from the Upper Devonian of Xinjiang, China and its bearing on the phylogenetic significance of the order Isoëtales

Abstract

Lepidostrobus xinjiangensis sp. nov. is described from Upper Devonian rocks of the eastern Junggar Basin, Xinjiang, north-west China. It provides new insights into the reproductive diversification and phylogenetic relationships of lycopsids in the Late Devonian. The strobilus shares more characteristics with arborescent lycopsids than any herbaceous forms, and falls within the diagnosis of Lepidostrobus . Each sporophyll consists of a deltoid pedicel and a triangular lamina. Sporophylls are horizontally inserted into the strobilus axis in low spirals. The pedicel, with lateral alations and an abaxial keel, extends distally into the upturned lamina and downturned heel, producing a peltate appearance. A single sporangium with terminal longitudinal dehiscence is a radially elongate, dorsiventrally flattened ovoid and is attached along its length to the adaxial surface of the pedicel. A column-like subarchesporial pad is found in the sporangium. A possible ligule occurs on the adaxial surface of the pedicel distal to the sporangium. The strobilus is microsporangiate, containing Lycospora -type spores with granulate ornamentation and an equatorial flange. Based on this new species, the reproductive diversification and evolutionary pattern in arborescent lycopsids from the Devonian through the Carboniferous are discussed in a phylogenetic framework. We suggest that the reproductive strategies represented by bisporangiate-and monosporangiate-strobili had proliferated by the Late Devonian, which implies that phylogenetically advanced arborescent lycopsids bearing Lepidostrobus strobili had an earlier origin than previously thought.

A new homosporous, arborescent lycopsid from the Middle Devonian of Xinjiang, Northwest China

“…Its character combination is noticeably different from the Mid–Late Devonian and Carboniferous arborescent lycopsids. Considering the large amount of heterosporous lycopsids from the Late Devonian (see Stewart and Rothwell 1993; Wang et al . 2003 b ), homosporous arborescent habit probably underwent a transient evolutionary stage that was by far only known from the Middle Devonian.…”

“…A rborescent lycopsids (or rhizomorphic lycopsids), probably originating from the herbaceous, homosporous protolepidodendralean lycopsids flourishing in the Middle Devonian (Stewart and Rothwell 1993; Kenrick and Crane 1997; Wang et al . 2003 b ), are thought to be evolutionary innovations in accelerating full colonization of land by plants and are most conspicuous pioneers in the Mid–Late Devonian to develop the arborescent habit and the heterospory (Algeo et al .…”

New perspective on the architecture of the Late Devonian arborescent lycopsid Leptophloeum rhombicum (Leptophloeaceae)

“…No in situ spores are known, although Lemoigne (1982) described a possible megaspore. Recently, Wang et al (2003c) described a new Lepidostrobus species from the Upper Devonian in Xinjiang, China, that also contained abundant L. rhombicum stem impressions in the same horizon, but there was no evidence for an organic connection between these two taxa. As for the rooting system, Li et al (1986) reported a 65 cm long Leptophloeum trunk, with a Stigmaria-type appearance of a 7.5 cm wide base, from the Upper Devonian in Xinjiang, China.…”

“…This suggests that diverse architecture of arborescent lycopsids might have undergone incipient radiations by the Frasnian of the Late Devonian. Longostachys latisporophyllus (Cai and Chen, 1996) from the Givetian and Chamaedendron multisporangiatum (Schweitzer and Li, 1996) from the Frasnian of China, despite their small size, possess a dichotomous rooting system and branching crown, which shows a close affinity to true arborescent lycopsids (Gensel and Berry, 2001;Berry and Fairon-Demaret, 2001;Wang et al, 2003c).…”

A new Late Devonian isoetalean lycopsid from New South Wales, Australia: Cymastrobus irvingii gen. et sp. nov

“…Wang et al (2003) proposed that Jurinodendron, together with Clevelandodendron ohioensis (Chitaley and Pigg, 1996) and Bisporangiotrobus harrisii (Chitaley and McGregor, 1988) represent the basal taxa of a supposedly monophyletic group that they referred to as the "Isoetales sensu stricto." This group would encompass the isoetalean lycopsids characterized by cormose rather than stigmarian rhizomorphs.…”