Marcano S Solenodon

Land plants constitute an important component of the Jehol Biota. They are recorded mainly from the Yixian Formation of West Liaoning, and represent almost all major groups of land plants known from the Mesozoic Era including free-sporing plants (Bryophyta, Lycopsida, Sphenopsida, Filicopsida) and seed plants (Ginkgoales, Czekanowskiales, Coniferales, Bennettitales, Gnetales and Angiospermae). This presentation is based mainly on the study of plant fossils from the Jianshangou Bed of the lower part of the Yixian Formation at Huangbanjigou, Beipiao City, western Liaoning. A total of species in 34 genera have been identified. Among these, 28 species and nine genera are new raxa. Below is a brief characteriza-tion of the major plants groups and where possible, their inferred paleoeco-

•n logical conditions will be also discussed.

Bryophytes Bryophytes (Bryophyta) are the most basal group among the land plants. They include small green plants of simple construction with untignified conducting tissue and without roots. They are distinguishable from all other land plants in having a dominant gametophyte and a very simple sporophyte that is born on the gametophyte (in other land plants the sporophyte is the dominant and the conducting tissue is lignified). The gametophyte is typically upright with dichotomous branching and small leaf-like appendages, or in liverworts it may be flattened and thalloid. The unbranched sporophyte is born on the gametophyte and produces a single terminal sporangium. Bryophytes mostly inhabit shady and humid environments, in the Jehol Biota they are represented by four species in two genera. Both leafy and thalloid types are present (Figs. 224, 225).

Lycopods Lycopsids (Lycopsida) have a basal position among the vascular plants. Extant lycopods are all herbaceous plants. They are characterized by having upright dichotomously branching stems growing from horizontal rhizomes and bearing densely spaced leaves. The plants arc heterosporous or homosporous and sporangia either grouped in small cones or scattered along the axes, born on the adaxial surface of leaf-like sporangiophylls. Lycopods have A wide ecological range with representatives in wet and humid environment as well as in arid regions. The three extant lycopod families, Lycopodiaceae, Selaginellaceae and Jsoeraceae, were also

Fossil Bryophyte

■ 225 Thallita riccioites, a bryophyte, 1.1 cm long, round print probably representing the regetative-reproductive organ gemma cups.

*im226 Lycapaditesfaustus, a lycopod, 5.95 cm long.

present in tin.- Oetaccous, but so far only members of t he Lycopodiaceae were recorded from the jehol Biota, such as LympoJitti fanstus, a homosporous plant with sporangia arranged in a strobilus (Figs. 226, 227).

Sphenopsids Sphenopsids or horsetails (Sphenopsida) are characterized by upright and distinctly articulate and typically hollow stems arising from horizontal rhizomes. Branches and leaves arc born in whorls at the nodes. The plants are hercrosporous or homosporous with terminal, mostly abuxial sporangia, born on peltate, scaly sporophylls that are arranged in terminal, ellipsoid cones. The only extant genus, Equtsttum (Ecjuisetaceae) is herbaceous and homosporous. It has very small leaves that are more or less fused to form a dentiform leaf sheath at the node. The surface of the internodes shows distinct longitudinal ridges from the vascular bundles. Equistlum predominately occurs in wet environments, and the hollow stems, characteristic also of many extinct sphenopsids, indicate that it was adapted to growth in moist areas Remnants of Equisetum-like plants, described as

w227 Enlargements of the lip of the specimen shown in Fig. 22f>, showing the strobili with two rows of round sporangia.

Equisetites, are very common in the fossil-bearing strata of the Yixian Formation. The most abundant sphenopsid in the Biota is Equisetite,r longevaginatus (Fig. 228), characterized by very small stem and rather long leaf sheath.

Filicopsids Filicopsids or ferns (Filicopsida) are the largest group of the free-sporing vascular plants. The plants have distinctly differentiated root, stem and leaves. They are woody or herbaceous and some attain tree habit, characterized by having an upright growth with a crown of large leaves. The leaves, often referred to as fronds, are simple or more commonly pinnately or dichotomously compound. Most terns are homosporous whereas a few are heterosporous. Sporangia are terminal born on the abaxial surface of normal or specialized leaves. Their position on the leaves is highly variable. They maybe scattered over the surface of the lamina or variously aggregated in circular, elongate or linear sori. Ferns mainly grow in humid and moist areas, but some are adapted to more arid conditions. Ferns are very common in the Yixian Formation and so far more than 5 species have been recognized. Particularly, species of the extinct genera Botrycbites (Figs. 229, 230), Eboracia (Fig. 231), and Coniopteris are conspicuous in the jehol plant assemblages.

Ginkgos Ginkgos (Ginkgoales) comprise large trees characterized by long shoots and short shoots. They have wood with small pith, proliferate helical branching and leaves born in a helical arrangement. Leaves on long shoots are typically widely spaced while those on the short shoots are clustered around rhe apical part. They are unique, fan-shaped with dichotomously branching veins, bilobed or sometime strongly dissected. The only extant species, Ginkgo biloba, is dioecious with female and male trees. The ovules and microsporophylls are terminal and born on the short shoots. The ovules are borne in small cups on a ovulate axis. Of typically two ovules in extant Ginkgo, only one reaches maturity. In some ancestral ginkgos ovules were more numerous on rhe ovulate axis. The ovules and mature seeds are relatively large with an outer fleshy layer. Ginkgos were much more abundant and diverse in the Mesozoic, particularly in the Late Jurassic and Early Cretaceous. Ginkgos declined drastically both in diversity and geographic distribution during the Late Cretaceous and Tertiary. During the Quaternary it became restricted to small areas in eastern China. The only known wild population of Ginkgo biloba is in a temperate moist forest of Zhejiang. Ginkgo biloba is mm 228 Equisetites longevaginatus, a sphenopsid. 3.7 cm long.

deciduous and the abundant occurrencc of leaves in certain geological horizons indicates chat at least some extinct ginkgos were also deciduous. In the Yixian Formation a single species of Ginkgo was reporred recently by /..-y. Zhou and S.-l. Zheng (2003) (Fig. 232), It is intermediate in the ovulate structure between modern Ginkgo and Jurassic ginkgos with many ovules. The flora also comprises several taxa belonging to extinct ginkgoalcan genera such as Ba/era (Fig. 233). Ginkgoites, and Sphtmhctma.

Czekanowskialeans Czekanowskialeans (Czekanowskiales) represent an extinct group of seed plants of unknown systematic affinity. It was

Botrychites

1229 Botrychites reheemis, a filicale, f>.8 cm long, showing the heteromorphic sterile and fertile pinna.

1230 Pinna of Botrychites reheensis, a filicale, -4 cm long.

1229 Botrychites reheemis, a filicale, f>.8 cm long, showing the heteromorphic sterile and fertile pinna.

1230 Pinna of Botrychites reheensis, a filicale, -4 cm long.

231 Sterile pinna of Eboracia lobifolia, a fiiicale, 1.8 cm long. Note the shape of the variant pinnule at the right of the base of pinna. (Photo: Shi-wet Zhao/ NICP)

1233 tiaiera borealis, a ginkgophyte, 7.1 cm long. (Photo:

Shi-wei Zhao/ NICP) mm234 Solenites murrayana, a ginkgophyte, 4.55 cm long.

231 Sterile pinna of Eboracia lobifolia, a fiiicale, 1.8 cm long. Note the shape of the variant pinnule at the right of the base of pinna. (Photo: Shi-wet Zhao/ NICP)

1233 tiaiera borealis, a ginkgophyte, 7.1 cm long. (Photo:

Shi-wei Zhao/ NICP) mm234 Solenites murrayana, a ginkgophyte, 4.55 cm long.

Ginkgo biloba

adianfcx'des Myr BP

Ginkgo biloba

mm232 Ginkgo apodes, a ginkgophyte, from Toudaohezi locality (7.huanchengi!i Bed ofYixian Formation) in Yixian, Liaoning. All scale bars = 5 mm. a, A juvenile ovulate organ with 6 collars and very short pedicels; b. Associated leaf: c, An ovulate organ bearing one nearly mature (red arrow) and probably one aborted ovule (blue arrow) and l~2(?) empty collars; d. Sketch reconstruction of the species and some other Ginkgo taxa. showing evolution of this group in geological history. (Courtesy: Zhi-yan Zhou/ NICP)

Cone ofSchizolepis beipiooensis, a conifer, 9.15 cm long.

Samara of Scluzolepis beipwoensis, a conifer. 1.15 cm long.

included in the Ginkgoales, but their leaves and their reproductive structures, particularly the ovulate structures, are distinct from those of Ginkgo, and they are now usually placed in a separate order. The leaves are borne in clusters on short shoots. They are very narrow and supplied by only a single vein, in contrast to rhe two veins that enter the leaves of Ginkgo. The leaves arc-typically dichotomized into several sections, each with a single vein. The ovulate structure called Leptostrobus is characterized by having elongated axes with bivalved ovule bearing units in a spiral arrangement. Each bivalved unit, often referred to as a capsule, contains several ovules. The microsporangiate structure, ¡xostrnbus, is a simple axis with pairs of pollen sacs also arranged in a spiral pattern. The Czekanowskiales were widespread and abundant during the Jurassic anil (.retaceous, particularly in floras of the Northern 1 lemisphere. In thejehol Biota species of Solcnita (Fig. 234) and Spbtttctrion are common Czekanowskialean elements.

Conifers Conifers (Coniferales) comprise trees or more rarely shrubs characterized by long shoots and short shoots. Wood is massive with small pith. Branching is proliferating and phyllotaxis is helical ur decussate. Leaves are homomorphic or hereromorphic, typically small needlelike, scaly or conical, supplied by a single vein or more rarely two veins. Most conifers arc monoecious. The ovules and microsporangia are terminal borne in cones. Ovulate cones are compound with ovules born on seed scale that is fused to the supporting cone scale. Mature seeds are usually rather small with a hard seed wall. Microsporangiate cones are simple and the pollen sacs are born on the abaxial surface of the microsporophylls. Conifers were abundant in the Mesozoic with many extinct forms occurring well into the Cretaceous. In the Yixian Formation all conifers so far recorded appear to belong to extinct genera and families. The most abundant conifer is Schtzokpis (Figs. 235, 236), but ELitacUiJui (Fig. 237) and Brachyphyllum also constitute an important part ol the jehol plant assemblage.

Bennettites Bennetritcs (Bennettitales) are extinct seed plants with a habit resembling that of the eveads both in the stature and in the morphology of leaves. Bennettites are reconstructed as small, sparsely branched or unbranched trees or small shrubs. The trunk is slender or in some bennettites barrel-shaped. Leaves are large, simple (entire) or pinnately divided, very similar in gross morphology to some cycad leaves. The two groups can, however, easily be distinguished by their epidermal features when present. The ovules and microsporophylls are crowded in rather large flowerlike structures that may be unisexual or bisexual. The ovules and mature seeds are minute and terminal densely spaced on a conical or spherical receptacle together with small interseminal scales. The microsporangia are borne on simple or branched (pinnate, bipinnate) microsporophylls. The bennettites were common in Triassic, Jurassic and Early Cretaceous strata but became cxtinut by the end of the Cretaceous. In the Yixian Formation four forms have been reported (Figs. 238—240).

Gnetales Gnetales comprise three extant genera (Ephedra, Gnetum, We/witscbia) that are morphologically very distinct. The phylogenetic posi-

u tion of tlie group is uncertain. It was sometimes placed close to the angiosperms, but has recently been associated with the conifers. Ephedra and Gnetum include trees, shrubs, vines and climbers with proliferate branching and decussate or whorled phyllotaxis. Welwitschia is unusual in having a very condensed, unbranched stem and two persistent leaves that grow for the entire life of the plant. The plants are mostly dioecious, rarely monoecious. The ovules and microsporophyUs are terminal borne in small compound, unisexual cones. The mature seeds are small to large. The microsporangia are borne in synangia. Ephedra is xerophytic and Wehvttscbia extreme xerophytic, while Gnetum is tropical genus with a wider ccological range inhabiting moist to rather dry environments. The fossil history of Gnetales is poorly known but Gnetales pollen occurs abundantly in Early Cretaceous sediments. In the Yixian Formation remnants of Gnetales are relatively common and several taxa have been described. Among these arc Eragrosites changii and L/aox/a chenii (Fig. 24 1) that was assigned to the extinct genus Ephedrites (Guo and

Wu, 2000), and Chaoyangia liangii (Fig. 242) assigned to the extinct genus Gurvanella (Sun et al,, 2001). They are all closely similar to Ephedra in their vegetative morphology, but some (e.g., Gurvanella) are distinguishable from Ephedra mi the ovulate structures.

Angiosperms Angiosperms (Angiospermae) are the most diverse of all plant groups and exhibit an enormous range in vegetarive and reproductive features. Probably the most distinct feature that distinguishes angiosperms from other plants is the enclosure of the ovules in carpellary tissue and pollen tube growth via the carpellary tissue to the ovules. Several angiosperms have been described (rom the Yixian formation but most of them are dubious (Figs. 243—250). Some have already been placcd in the Gnetales, while the features of others such as Archaejructus is still debated (see the Chapter "Angiosperms"). A more distinct angiosperm was described recently by Qin Leng and Else M. Friis and will be treated in the next chapter together with a discussion on the Jehol angiosperms.

(Unless otherwise stated, fossils shown in this chapter are collected from thejianshangou Bed of the lower part of the Yixian Formation at Huangbanjigou, Beipiao, Liaoning, photo by Da-jian Li/ CAS)

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1239 Rehezamites anisolobus, a possible bennettite, 10,1 cm long [Left).

1240 Tyrmia acrodonla, a bennettite, 6.9 cm long (Right)

Bennettites

wb 241 Liaoxin chenii, a gnetale, 8.9 cm long. (Photo: Dong-xing Deng/ NIGP)

wKm; % ¡¿del iM

¡245 Leaf shoot of Utiles reheensis, Plantae incertae sedis. 9.8 cm lung, showing opposite and amplexicaul leaves, and arching veins.

i246 Fruit spur of Lilites reheensis, Plantae incertae sedis, 4.5 cm long, showing terminal fruit and opposite leaves.

Beipiao Fossil Fruit
i249 Antholithus sp. 1. Plantae incertae sedis, 3.1 cm long. {Photo: Dong-xing Deng/ NIGP)

1.250 Antholithus sp. 2, Plantae incertae sedis. 3.5 cm long. (Photo: Shi-wei Zhao/ NIGP)

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