Hong-He Xu

Complex Branching Patterns in a Newly Recognized Species of Compsocradus Berry et Stein (Iridopteridales) from the Middle Devonian of North Xinjiang, China

Specimens, including the largest known axes, of an iridopteridalean plant of late Middle Devonian age are described from northern Xinjiang, China. The plant consists of three orders branching and dichotomous appendages. The first-order axis probably represents the stem. Lateral organs (lower-order branches and appendages) are attached along the primary axis in up to 10 ranks. The insertion pattern can be broken down into cycles in which one lateral is inserted in each rank, and each cycle is divided into two loose whorls; in one loose whorl, laterals occur in about half of the ranks, some adjacent, and in the other loose whorl, laterals occur in the other ranks. These ranks are believed to map the position of xylem ribs of the vascular system, which has not been preserved. The appendages are isodichotomously divided up to five times. Pairs of recurved sporangia terminate the fertile appendages. A collection of small axes (second and third order) of this plant from the same locality, lacking the distinctive branching patterns displayed in our first order axes, was recently given the name Ramophyton givetianum by D. M. Wang. Our enlarged concept of the plant includes several morphological similarities to Compsocradus laevigatus Berry et Stein from Venezuela, particularly relating to the branching pattern. The Xinjiang plant is therefore reassigned to Compsocradus givetianus (Wang DM) Fu, Wang Y, Berry et Xu comb. nov. It further increases knowledge of branching patterns amongst Iridopteridales, important for evaluating relationships to other plant groups.

A New Species of Leclercqia Banks, Bonamo et Grierson (Lycopsida) from the Middle Devonian of North Xinjiang, China, with a Possible Climbing Habit

A new herbaceous lycopsid species, Leclercqia uncinata Xu, Berry, Wang et Marshall, is established on the basis of compression fossils from the Middle Devonian of Xinjiang, NW China. The new species has slender axes and three-dimensional, seven-tipped leaves with a distally hooked central segment conforming to the original diagnosis of the genus, and it is relatively smaller than the type species, L. complexa from New York State. The sporangium contains the spore, which can be assigned to morphotaxon Acinoporites lindlariensis. In our preparation of compressions, iridopteridalean fertile appendages are found trapped between the distally hooked leaves of L. uncinata. A possible climbing habit of the new plant is discussed.

Report of Drepanophycus Göppert (Lycopsida) from the Middle Devonian of Xinjiang, China

The herbaceous lycopsid Drepanophycus minor sp. nov. is described from the late Mid Devonian Hujiersite Formation of Xinjiang, Northwest China. The new species is characterized by minor sized, falcate microphylls, and kidney‐shaped sporangia, with rhizome, K‐shaped branching, and developed lateral buds. Stomatal apparatuses are observed from the axis surface of the new species. The habit and the rhizome structure of D. minor are discussed.

A New Species of Aneurophyton (Progymnospermopsida) from the Middle Devonian of West Junggar, Xinjiang, China, and Its Paleophytogeographical Significance

Aneurophyton doui sp. nov. (Aneurophytales, Progymnospermopsida) is described from the late Middle Devonian Hujiersite Formation of Hoxtolgay, Xinjiang, northwest China, as a plant with at least four orders of axes and ultimate units (vegetative appendages/fertile organs). Spines cover the surface of all orders of axes and ultimate units. The second-order axes and the vegetative appendages are closely inserted in pairs and helically arranged. From the second order, axes of subsequent orders are produced by bifurcation. The vegetative appendages are unwebbed and up to three times dichotomous. The fertile organ is pinnate, and the fertile organ axes are opposite or subopposite with adaxial, elliptical sporangia. This is the first formal report of Aneurophyton beyond the coasts of the Rheic Ocean. West Junggar, the locality of present species of Aneurophyton, played a key role in the dispersal of Aneurophytales in the Middle Devonian.

Leaf evolution in early-diverging ferns: insights from a new fern-like plant from the Late Devonian of China.

BACKGROUND AND AIMS With the exception of angiosperms, the main euphyllophyte lineages (i.e. ferns sensu lato, progymnosperms and gymnosperms) had evolved laminate leaves by the Late Devonian. The evolution of laminate leaves, however, remains unclear for early-diverging ferns, largely represented by fern-like plants. This study presents a novel fern-like taxon with pinnules, which provides new insights into the early evolution of laminate leaves in early-diverging ferns. METHODS Macrofossil specimens were collected from the Upper Devonian (Famennian) Wutong Formation of Anhui and Jiangsu Provinces, South China. A standard degagement technique was employed to uncover compressed plant portions within the rock matrix. KEY RESULTS A new fern-like taxon, SHOUGANGIA BELLA GEN ET SP NOV: , is described and represents an early-diverging fern with highly derived features. It has a partially creeping stem with adventitious roots only on one side, upright primary and secondary branches arranged in helices, tertiary branches borne alternately or (sub)oppositely, laminate and usually lobed leaves with divergent veins, and complex fertile organs terminating tertiary branches and possessing multiple divisions and numerous terminal sporangia. CONCLUSIONS Shougangia bella provides unequivocal fossil evidence for laminate leaves in early-diverging ferns. It suggests that fern-like plants, along with other euphyllophyte lineages, had independently evolved megaphylls by the Late Devonian, possibly in response to a significant decline in atmospheric CO2 concentration. Among fern-like plants, planate ultimate appendages are homologous with laminate pinnules, and in the evolution of megaphylls, fertile organs tend to become complex.

Unique growth strategy in the Earth's first trees revealed in silicified fossil trunks from China

Significance The evolution of trees and forests in the Mid–Late Devonian Period, 393–359 million years ago, profoundly transformed the terrestrial environment and atmosphere. The oldest fossil trees belong to the Cladoxylopsida. Their water-conducting system is a ring of hundreds of individual strands of xylem (water-conducting cells) that are interconnected in many places. Using anatomically preserved trunks, we show how these trees could grow to a large size by the production of large amounts of soft tissues and new wood around the individual xylem strands and by a controlled structural collapse at the expanding base. We have discovered a complex tree growth strategy unique in Earth history, but with some similarity to that of living palms. Cladoxylopsida included the earliest large trees that formed critical components of globally transformative pioneering forest ecosystems in the Mid- and early Late Devonian (ca. 393–372 Ma). Well-known cladoxylopsid fossils include the up to ∼1-m-diameter sandstone casts known as Eospermatopteris from Middle Devonian strata of New York State. Cladoxylopsid trunk structure comprised a more-or-less distinct cylinder of numerous separate cauline xylem strands connected internally with a network of medullary xylem strands and, near the base, externally with downward-growing roots, all embedded within parenchyma. However, the means by which this complex vascular system was able to grow to a large diameter is unknown. We demonstrate—based on exceptional, up to ∼70-cm-diameter silicified fossil trunks with extensive preservation of cellular anatomy from the early Late Devonian (Frasnian, ca. 374 Ma) of Xinjiang, China—that trunk expansion is associated with a cylindrical zone of diffuse secondary growth within ground and cortical parenchyma and with production of a large amount of wood containing both rays and growth increments concentrically around individual xylem strands by normal cambia. The xylem system accommodates expansion by tearing of individual strand interconnections during secondary development. This mode of growth seems indeterminate, capable of producing trees of large size and, despite some unique features, invites comparison with secondary development in some living monocots. Understanding the structure and growth of cladoxylopsids informs analysis of canopy competition within early forests with the potential to drive global processes.

A diminutive plant from the Late Silurian of Xinjiang, China

A new diminutive plant, Filiformorama simplexa gen. et sp. nov., is described from the Late Silurian (late Pridoli) Wutubulake Formation of north Xinjiang, China and is placed tentatively in the rhyniophytoids. This plant has naked axes and a dichotomous branching system. A body, interpreted as a sporangium, forms the termination of one branch of a dichotomy, and the other daughter branch continues to grow and dichotomizes further. Most complete sporangia are circular, but some are reniform or tongue-shaped, with an asymmetric base.A new diminutive plant, Filiformorama simplexa gen. et sp. nov., is described from the Late Silurian (late Pridoli) Wutubulake Formation of north Xinjiang, China and is placed tentatively in the rhyniophytoids. This plant has naked axes and a dichotomous branching system. A body, interpreted as a sporangium, forms the terminatation of one branch of a dichotomy, and the other daughter branch continues,to grow and dichotomizes further. Most complete sporangia are circular, but some are reniform or tongue-shaped, with an asymmetric base.

Notes on a fertile rhyniophytoid from the Lower Devonian of Guangxi, southwestern China

A fertile rhyniophytoid is discovered from the Lower Devonian of Guangxi, southwestern China, which is characterised by small size, dichotomous branchings and terminal sporangia. This plant is similar to the genus Aberlemnia Gonez et Gerrienne and also, is comparable to some mesofossil morphotypes of early land plants from the Early Devonian (Lochkovian) Old Red Sandstone floras. This study adds new data to the generally zosterophyll-dominated Early Devonian floras of South China and sheds some lights on the palaeophytogeography of rhyniophytoids.

Reinvestigation of the Late Devonian Shougangia bella and new insights into the evolution of fern-like plants

Shougangia bella from the Late Devonian (Famennian) of South China is a fern-like plant known for its morphology and now provided with anatomy and a reconstruction. Its stems contain a dissected stele with a four-ribbed and an elongate-curved primary xylem segments changing to three elongate and slightly curved segments. Primary branches have a dissected stele with three similar primary xylem segments as in stems. The primary xylem of the stems and primary branches is mesarch, and individual primary xylem segments bear peripheral protoxylem strands and are surrounded by secondary xylem. Shougangia is anatomically compared with fern-like plants, zygopterid ferns and early seed plants, verifying its uncertain affinity at class and order levels as suggested by morphology, or representing a new order within the Cladoxylopsida. On the basis of anatomy and branching pattern, it is emphasized that most fern-like plants appear evolutionarily closely related to iridopteridaleans. Secondary xylem is involved not only in mechanical support, but also more likely in enhancing water supply for fern-like plants including Shougangia. By the Late Devonian, besides the abrupt drop of atmospheric CO2 levels, the presence of secondary xylem may correlate well with the primary radiation of leaves (megaphylls) of euphyllophytes (e.g. fern-like plants, sphenopsids, progymnosperms and seed plants).

A new lycopsid from the Lower Carboniferous of Nanjing, South China

Biformistrobus wui gen. et sp. nov. is described from the uppermost part of the Wutung Formation (Tournaisian, Early Carboniferous) of Kongshan, Nanjing, South China, as a lycopsid bearing a stem up to 17 mm wide, spirally arranged, narrowly obovate leaf bases, and linear to lanceolate leaves. Stems are multi-dichotomously branched, bearing two different strobili on distal tips, but the anatomical features and in situ spores are unknown. In light of the single-veined microphylls, relatively thin axes, adaxially attached sporangium on the sporophylls, and dimorphic strobili, Biformistrobus probably represents either a part of a monoecious, herbaceous lycopsid or a portion of distal branching systems from a heterosporous, arborescent lycopsid. Biformistrobus is probably endemic in the Early Carboniferous flora of South China.