Yong Yang

Schmeissneria: A missing link to angiosperms?

BackgroundThe origin of angiosperms has been under debate since the time of Darwin. While there has been much speculation in past decades about pre-Cretaceous angiosperms, including Archaefructus, these reports are controversial. The earliest reliable fossil record of angiosperms remains restricted to the Cretaceous, even though recent molecular phylogenetic studies suggest an origin for angiosperms much earlier than the current fossil record.ResultsIn this paper, after careful SEM and light microscopic work, we report fossils with angiospermous traits of the Jurassic age. The fossils were collected from the Haifanggou Formation (middle Jurassic) in western Liaoning, northeast China. They include two female structures and an associated leaf on the same slab. One of the female structures is physically connected to the apex of a short shoot. The female organs are borne in pairs on short peduncles that are arranged along the axis of the female structure. Each of the female organs has a central unit that is surrounded by an envelope with characteristic longitudinal ribs. Each central unit has two locules completely separated by a vertical septum. The apex of the central unit is completely closed. The general morphology places these fossils into the scope of Schmeissneria, an early Jurassic genus that was previously attributed to Ginkgoales.ConclusionBecause the closed carpel is a character only found in angiosperms, the closed apex of the central unit suggests the presence of angiospermy in Schmeissneria. This angiospermous trait implies either a Jurassic angiosperm or a new seed plant group parallel to angiosperms and other known seed plants. As an angiosperm, the Liassic age (earliest Jurassic) of Schmeissneria microstachys would suggest an origin of angiosperms during the Triassic. Although still uncertain, this could have a great impact on our perspective of the history, diversity and systematics of seed plants and angiosperms.

The earliest fleshy cone of Ephedra from the early cretaceous Yixian Formation of northeast China.

Bracts of female cones of extant gymnosperm Ephedra (Joint fir) are either colorful and fleshy (section Ephedra), or dry-winged and membranous (section Alatae), or dry and coriaceous (section Asarca), which have played a crucial role in long-distance seed dispersal that is responsible for a wide distribution of the genus in semiarid and arid areas of Eurasia, North Africa, North America, and South America. Recent molecular systematic studies on Ephedra have suggested that the fleshy bracts in character evolution may be plesiomorphic relative to the dry, membranous and coriaceous bracts. However, little is known about when the fleshy bracts of Ephedra have made their debut in the geological past. Herein, we describe a novel, fleshy bract-bearing female cone macrofossil from the Early Cretaceous (ca. 120—125 Ma) Yixian Formation in Liaoning, northeastern China. This cone bears three ellipsoid seeds subtended by only one whorl of fleshy bracts. Each seed has a thin outer envelope and an inner integument that extends upward and passes through the opening of the outer envelope, forming a thin and straight micropylar tube. Such a syndrome shows the closest similarity to an extant triovulate species Ephedra intermedia in the section Ephedra, but the latter bears a whorl of terminal fertile bracts and more than one whorl of inferior sterile bracts, and a thick outer envelope. Hence, we establish a new fossil species Ephedra carnosa. Our discovery provides the first direct macrofossil evidence for the previous molecular systematics of Ephedra, implying that the origin of fleshy bracts in Ephedra should not have been later than that of the membranous and coriaceous bracts by at least the Early Cretaceous.

Asymmetrical development of biovulate cones resulting in uniovulate cones in Ephedra rhytidosperma (Ephedraceae)

Female cone morphology in Ephedra, including the number of initiated ovules and mature seeds per cone, provides important taxonomic characters used in sectional or species delimitation within Ephedra. Recent molecular phylogenies have indicated, however, that seed number per cone has changed repeatedly during the evolution of the genus. This study reports on the development of the female cone of E. rhytidosperma, based on a large sample of dissected cones studied under SEM. All cones were initially biovulate, and in the majority of cases, both female reproductive units (FRUs) developed a micropylar tube and formed mature seeds. In a few cases, the FRU pair developed asymmetrically in a cone, with one of them eventually aborting. There was no evidence of fusion of the FRU pair. Phylogenetically, E. rhytidosperma is in a clade with E. equisetina, which has uniovulate cones, and E. gerardiana and E. minuta, which have biovulate cones that also become unispermous via abortion. The biovulate condition may thus be ancestral in this clade.

Chengia laxispicata gen. et sp. nov., a new ephedroid plant from the Early Cretaceous Yixian Formation of western Liaoning, Northeast China: evolutionary, taxonomic, and biogeographic implications

BackgroundThe extant Gnetales include three monotypic families, namely, Ephedraceae (Ephedra), Gnetaceae (Gnetum), and Welwitschiaceae (Welwitschia), all of which possess compound female cones that comprise a main axis and 1 to multiple pairs/whorls of bracts subtending a female reproductive unit or having lower pairs/whorls of bracts sterile. However, the evolutionary origin of such a reproductive architecture in Gnetales is controversial in the light of the competing anthophyte versus gnetifer hypotheses of seed plant relationships. Hence, macrofossils demonstrating the structure of compound female cones of the Gnetales should be important to decipher the early evolution of the order.ResultsA new ephedroid plant Chengia laxispicata gen. et sp. nov. is described from the Early Cretaceous Yixian Formation of western Liaoning, Northeast China. The fossil represents a part of a leafy shooting system with reproductive organs attached. The main shoot bears internodes and swollen nodes, from which lateral branches arise oppositely. Reproductive organs consist of female spikes terminal to twigs or axillary to linear leaves. Spikes are loosely arranged, having prominent nodes and internodes. Bracts of the spikes are decussately opposite and comprise 4—8 pairs of bracts. Each bract subtends an ellipsoid seed. Seeds are sessile, with a thin outer envelope and a distal micropylar tube.ConclusionsChengia laxispicata gen. et sp. nov. provides a missing link between archetypal fertile organs in the crown lineage of the Gnetales and compound female cones of the extant Ephedraceae. Combined with a wealth of Ephedra and ephedroid macrofossils from the Early Cretaceous, we propose a reduction and sterilization hypothesis that the female cone of the extant Ephedraceae may have stemmed from archetypal fertile organs in the crown lineage of the Gnetales. These have undergone sequentially intermediate links similar to female cones of Cretaceous Siphonospermum, Chengia, and Liaoxia by reduction and sterilization of the lower fertile bracts, shortenings of internodes and peduncles as well as loss of reproductive units in all inferior bracts. The basal family Ephedraceae including Ephedra of the extant Gnetales was demonstrated to have considerable diversity by the Early Cretaceous, so an emended familial diagnosis is given here. The Jehol Biota in Northeast China and adjacent areas contains a plethora of well-preserved macrofossils of Ephedra and ephedroids that show different evolutionary stages including primitive and derived characters of Ephedraceae, so Northeast China and adjacent areas may represent either the centre of origination or one of the centres for early diversification of the family.

The nomenclature of fossil Ephedraceae

A review of recently published fossil Ephedraceae reveals a number of nomenclatural problems. Liaoxia Cao & S.Q. Wu and Liaoxia chenii Cao & S.Q. Wu were not validly published by Cao & S.Q. Wu in 1998 when they first described the fossils concerned. However, Liaoxia Cao & S.Q. Wu was validly published by Rydin, Wu & Friis in 2006 and Liaoxia cheniae (as chenii) was also validly published by them, but as a new combination based on Ephedrites cheniae Guo & Wu (as chenii), validly published in 2000, and should be cited as Liaoxia cheniae (Guo & Wu) Cao & S.Q. Wu in Rydin & al. The epithet is corrected to cheniae because it commemorates a lady, Prof. Chen Shouliang. The continued use of Ephedrites Gopp. & Berendt is recommended because of its straightforward meaning and long history of usage, providing nomenclatural stability. Transfer to Ephedrites of names recently published in Liaoxia is deferred until a recommendation is made on the recent proposal to conserve Ephedrites with a new type.

Leaf Cuticular Anatomy and Taxonomy of Syndiclis (Lauraceae) and its Allies

Abstract— n We studied leaf cuticles of 48 species of Beilschmiedia, Endiandra, Potameia, Sinopora, and Syndiclis from eastern Asia and Madagascar using light microscopy and scanning electron microscopy. This study shows that leaf cuticles of Lauraceae possess characters useful in taxonomy, including the ornamentation of periclinal walls, straightness and uniformity of thickness of anticlinal walls, stomatal ledges, and surface of the stomatal complex. The stomatal ledges and the surface of the stomatal complex are valuable in supraspecific grouping while ornamentation of periclinal walls, thickness and straightness of anticlinal walls, and presence/absence of round oil deposits are applicable to species identification. Leaf cuticular features together with veinlet anatomy and macromorphology (e.g. terminal buds) were tentatively applied to classify the Asiatic Beilschmiedia group. Five groups are recognized, namely the Beilschmiedia delicata group, the B. glauca group, the B. intermedia group, the Endiandra group, and the Syndiclis group, each of which shares a suit of cuticular characters. Syndiclis (at least the Chinese species) consists of closely related species with a common origin and has not been derived several times independently from Beilschmiedia. Venation type and cuticular characters support a close relationship between Sinopora and Syndiclis. Sinopora hongkongensis is close to Syndiclis pingbienensis.

A genome for gnetophytes and early evolution of seed plants

Gnetophytes are an enigmatic gymnosperm lineage comprising three genera, Gnetum, Welwitschia and Ephedra, which are morphologically distinct from all other seed plants. Their distinctiveness has triggered much debate as to their origin, evolution and phylogenetic placement among seed plants. To increase our understanding of the evolution of gnetophytes, and their relation to other seed plants, we report here a high-quality draft genome sequence for Gnetum montanum, the first for any gnetophyte. By using a novel genome assembly strategy to deal with high levels of heterozygosity, we assembled >4 Gb of sequence encoding 27,491 protein-coding genes. Comparative analysis of the G. montanum genome with other gymnosperm genomes unveiled some remarkable and distinctive genomic features, such as a diverse assemblage of retrotransposons with evidence for elevated frequencies of elimination rather than accumulation, considerable differences in intron architecture, including both length distribution and proportions of (retro) transposon elements, and distinctive patterns of proliferation of functional protein domains. Furthermore, a few gene families showed Gnetum-specific copy number expansions (for example, cellulose synthase) or contractions (for example, Late Embryogenesis Abundant protein), which could be connected with Gnetum’s distinctive morphological innovations associated with their adaptation to warm, mesic environments. Overall, the G. montanum genome enables a better resolution of ancestral genomic features within seed plants, and the identification of genomic characters that distinguish Gnetum from other gymnosperms.The evolution and phylogenetic placement of gnetophytes have remained elusive. The draft genome for a gnetophyte, Gnetum montanum, is now reported. Comparative analyses identify genomic features distinguishing gnetophytes from other gymnosperms.

Parallel evolution of leaf morphology in gnetophytes

In the present paper, an ephedroid macrofossil species from the Early Cretaceous Yixian Formation of western Liaoning of China is described as new to science: Ephedra multinervia Yang et Lin, sp. nov. This species has typical ephedroid morphology, e.g. the dichasial branching shoot system, swollen nodes, internodes having many fine longitudinal striations and opposite phyllotaxy. Ephedra multinervia has strap-shaped leaves with multiple dichotomizing veins and reduced female cones with a single pair of fertile bracts forming a cupule enclosing two inner seeds. Ephedra multinervia is similar to Ephedra archaeorhytidosperma Yang et al. and Ephedra hongtaoi Wang et Zheng in its reduced bi-ovulate female cone, but differs from the latter two species by the lengthy strap-like leaves bearing multiple parallel veins and its sessile female cones. A new evolutionary hypothesis of the gnetophytes is proposed based on a synthesis of reproductive morphology of macrofossils from the Early Cretaceous and modern representatives. A Chengia-like precursor might have given rise to the Gnetum-Welwitschia clade by diversification of leaf morphology and female reproductive organs. According to this new explanation, the Welwitschia-like strap-like leaves with multiple parallel veins in E. multinervia result from convergence.

New insights into the species problem

Historical opinions of the “species problem” are briefly reviewed, and four salient stages are recognized according to origin of species concepts. We propose that species is the unit preserving superior gene assembly and is maintained by specific mechanisms. Based on characteristics of plant evolution, we assume that understanding plant species may include three stages, i.e. morphological recognition stage, multidisciplinary verification stage, and illuminating mechanisms preserving superior gene assembly.

A new species of Ephedra L. (Ephedraceae) from Sichuan, China with a note on its systematic significance

A new species, Ephedra dawuensis Y. Yang, is described and illustrated. This species is similar to E. equisetina Bunge in having thin branchlets 0.8-1 mm in diam. and brown scale-like leaves, and to E. saxatilis Royle ex Florin in having oblong-ellipsoid seeds and a short micropylar tube ca. 0.5 mm long. It differs from E. equisetina in having female cones bearing 2 or 3 pairs of bracts (vs. 4 or 3 pairs of bracts), purplish black, oblong-ellipsoid seeds (vs. ovoid seeds), and a shorter micropylar tube (vs. 1.5-2 mm long), and from E. saxatilis in having thinner branchlets and brown scale-like leaves (vs. yellowish, narrow triangular, leaves). This new species is assigned to E. sect. Ephedra in that the bracts of female cones become fleshy at maturity. Intermediate character states of this new species provide evidence for the hypothesized affinity between E. equisetina and E. saxatilis.