A new Late Devonian genus with seed plant affinities

Abstract

BackgroundMany ovules of Late Devonian (Famennian) seed plants have been well studied. However, because few taxa occur with anatomically preserved stems and/or petioles, the vascular system of these earliest spermatophytes is little understood and available data come mostly from Euramerica. There remains great controversy over the anatomical differentiation of Late Devonian and Carboniferous seed plant groups of Buteoxylonales, Calamopityales and Lyginopteridales. Protostele evolution of these early spermatophytes needs more research.ResultsA new taxon Yiduxylon trilobum gen. et sp. nov. with seed plant affinities has been discovered in the Upper Devonian (Famennian) Tizikou Formation of Hubei Province, China. It is represented by stems, helically arranged and bifurcate fronds with two orders of pinnae and planate pinnules. Both secondary pinnae and pinnules are borne alternately. Stems contain a small protostele with three primary xylem ribs possessing a single peripheral protoxylem strand. Thick secondary xylem displays multiseriate bordered pitting on the tangential and radial walls of the tracheids, and has biseriate to multiseriate and high rays. A narrow cortex consists of inner cortex without sclerotic nests and sparganum-type outer cortex with peripheral bands of vertically aligned sclerenchyma cells. Two leaf traces successively arise tangentially from each primary xylem rib and they divide once to produce four circular-oval traces in the stem cortex. Four vascular bundles occur in two C-shaped groups at each petiole base with ground tissue and peripheral bands of sclerenchyma cells.ConclusionsYiduxylon justifies the assignment to a new genus mainly because of the protostele with protoxylem strands only near the periphery of primary xylem ribs, leaf trace origination and petiolar vascular supply structure. It shares many definitive characters with Calamopityales and Lyginopteridales, further underscoring the anatomical similarities among early seed plants. The primary vascular system, pycnoxylic-manoxylic secondary xylem with bordered pits on both tangential and radial walls of a tracheid and leaf trace divergence of Yiduxylon suggest transitional features between the early spermatophytes and ancestral aneurophyte progymnosperms.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0292-6) contains supplementary material, which is available to authorized users.

Buried deep beyond the veil of extinction: Euphyllophyte relationships at the base of the spermatophyte clade

“…Our analysis (Analysis 2) recovers an aneurophyte clade (exclusive of Reimannia aldenense and Triloboxylon arnoldii , both classified at least tentatively as aneurophytes—see below), a Stenokoleales clade (including Gothanophyton zimmermanni , a plant of unresolved affinities), and a seed plant clade (exclusive of Yiduxylon trilobum , which was discussed as a putative seed plant; Wang and Liu, ). Recovery of an aneurophyte clade is in contrast to the results of the only previous analysis that included more than one aneurophyte progymnospmerm (Momont, ), which recovered aneurophytes as a paraphyletic group.…”

“…For instance, not all species classified as progymnosperms (therefore, lignophytes) have been demonstrated to possess secondary growth, let alone from a bifacial cambium; additionally, reproductive structures are not known for all the species placed among progymnosperms (Bonamo, ; Beck, ). Likewise, most of the earliest species classified as seed plants preserve no evidence of reproductive structures to ascertain their seed plant identity (e.g., Galtier and Meyer‐Berthaud, ; Dunn and Rothwell, ; Wang and Liu, ). Furthermore, for the Stenokoleales, little is known about the architecture and anatomy of their branching systems and no reproductive structures have been documented (Beck, ; Matten and Banks, ; Matten, ; Momont et al., ).…”

Further study of Late Devonian seed plant Cosmosperma polyloba: its reconstruction and evolutionary significance

“…Vegetative fronds have been reported in the Late Devonian seed plants, i.e., Elkinsia from USA [5], Laceya from Ireland [17, 18], Kongshania [8], Yiduxylon [13] and Telangiopsis [10] from China. Among them, Elkinsia , Kongshania and Telangiopsis are also known for fertile rachises with terminal pollen organs.…”

“…Other evidence that supports lyginopterids as vines/lianas includes stems bearing long internodes, the presence of adventitious roots, large fronds with swollen frond bases, wide angle of frond attachment and Dictyoxylon -type outer cortex [13, 37, 38]. Cosmosperma possesses relatively large fronds with pulvinus-shaped bases, which resemble those of lyginopterids.…”

Latisemenia longshania , gen. et sp. nov., a new Late Devonian seed plant from China

“…Pseudosporogonites bertrandii [4]), and are known for pollen organs [43][44][45] or anatomy of seed plant branches [43,[46][47][48][49]. Recently, the Famennian Cosmosperma (cupules and pollen organs) [5], Kongshania (pollen organs) [50], Placotheca (pollen organs) [51] and Yiduxylon (vegetative branches with anatomy) [52] have been reported from South China. These fertile and vegetative organs, now including ovules of Latisemenia, indicate that the earliest seed plants were more widely distributed than was previously understood.…”