REPRODUCTIVE BIOLOGY OF THE CERRO CUADRADO (JURASSIC) FOSSIL CONIFERS: PARARAUCARIA PATAGONICA

Seventy-two silicified cone specimens of Pararaucaria patagonica Wieland from the Cerro Cuadrado (Jurassic) petrified forest in Patagonia were studied by use of thin sections and reflected light. Traces from the cone axis stele to the bract and ovuliferous scale are separate at their origins. In cross section the abaxially concave ovuliferous scale trace and massive circular bract trace branch half-way out into the cone-scale complex. Two triangular-shaped bundles of fibers follow the scale trace into the laminar part of the ovuliferous scale. Both surfaces of the ovuliferous scale possess hairs which may have assisted in cone closure. Cones typically contain one flattened, winged seed per ovuliferous scale. Multi-layered seed integuments are represented by an inner fleshy layer of large cells filled with a black amorphous material, a sclerotesta consisting of wedges or fan-shaped groups of sclereids oriented at right angles to the seed surface, and a thin, often crushed fleshy layer. Seed wings consist of anastomosing, branched cells resembling glandular hairs and containing many intercellular spaces. Well-preserved polycotyledonous embryos containing up to eight cotyledons are present in several cones. Tissues of the embryo including the shoot apex, calyptroperiblem, hypocotyl, and cotyledons are described. On the basis of anatomical and morphological features, specimens of P. patagonica are compared to members of both extant and extinct families of conifers including the Araucariaceae, Taxodiaceae, Pinaceae, Cupressaceae, and Cheirolepidaceae.     

The seed cone Eathiestrobus gen. nov.: Fossil evidence for a Jurassic origin of Pinaceae

? Premise of the study: Pinaceae and nonpinoid species are sister groups within the conifer clade as inferred from molecular systematic comparisons of living species and therefore should have comparable geological ages. However, the fossil record for the nonpinoid lineage of extant conifer families is Triassic, nearly 100 million years older than the oldest widely accepted Lower Cretaceous record for Pinaceae. An anatomically preserved fossil conifer seed cone described here extends the stratigraphic range of Pinaceae nearly 30 million years, thus reducing the apparent discrepancy between evidence from the fossil record and inferences from systematic studies of living species. ? Methods: Material was prepared as serial thin sections by the cellulose acetate peel technique, mounted on microscope slides, and viewed and photographed using transmitted light. ? Key results: A large cylindrical cone consisting of bract-scale complexes that diverge from the cone axis in a helical phyllotaxis has bracts and scales that separate from each other in the midregion and are of equal length and of nearly equal width. The cone has two inverted and winged seeds that are attached to the adaxial surface of each cone scale and, thus, represents an early member of the Pinaceae. ? Conclusions: Eathiestrobus mackenziei gen. et sp. nov. extends the fossil record for well-documented members of the family Pinaceae from the Lower Cretaceous to the Kimmeridgian Stage of the Upper Jurassic. This species also clarifies the set of characters that are diagnostic for seed cones of Pinaceae and reveals possible plesiomorphic characters for seed cones of the family.     

On the genus Tomaxellia (Coniferae) from the Lower Cretaceous of Patagonia (Argentina) and its male and female cones

This paper reports the organic attachment of male and female cones to twigs previously described as Tomaxellia biforme Archangelsky. The male cones produce Classopollis pollen, while the scales of the female structures are comparable to the Rhaeto-Liassic northern genus Cheirolepidium. A new interpretation of the possible female cone of Cheirolepidium is presented, based on the new evidence now available with the knowledge of Tomaxellia cones. Other female cones found in Mesozoic formations may be comparable to some extent with Tomaxellia , such as Indostrobus (Cretaceous of India) or Pararaucaria (Jurassic of Argentina), and they may be grouped in the family Cheirolepidiaceae. Comparisons with older conifer genera with known female cones are also included (Voltziaceae). Some morphological changes of the female cones, which probably took place during the Mesozoic (in these particular groups) are also inferred.     

AGAMOUS subfamily MADS-box genes and the evolution of seed cone morphology in Cupressaceae and Taxodiaceae

In this comparative developmental genetics study, we test hypotheses based on fossil and morphological data on reproductive organ morphology and evolution in conifers--specifically, the ovule-bearing organ in Cupressaceae and Taxodiaceae. Genes homologous to the Arabidopsis gene AGAMOUS are expressed in ovuliferous scales of spruces (Picea) throughout development. Previous studies have shown that the AGAMOUS subfamily of MADS-box genes predates the split between angiosperms and gymnosperms, and that these genes have in part conserved functions in reproductive development among seed plants, especially in the specification of identity of the ovule-bearing organs. These data indicate that their expression in conifer families other than Pinaceae might be used as markers for organs homologous to the Pinaceae ovuliferous scale. Here we have isolated putative AGAMOUS orthologs from Cupressaceae and Taxodiaceae and analyzed their expression pattern in seed cones to test for the presence of morphological homologs of ovuliferous scales. Our results were not congruent with the hypothesis that the tooth of the Cryptomeria seed cone is homologous to the Picea ovuliferous scale. Likewise, the hypothesis that the bracts of Thujopsis and Juniperus contain fused ovuliferous scales was not supported. However, we found expression of AGAMOUS homologs in the sterile bracts of Cupressaceae seed cones at late developmental stages. This expression probably represents a novel gene function in these conifer families, since no corresponding expression has been identified in Pinaceae. Our study suggests that the evolutionary history of modern conifer cones is more diverse than previously thought.     

Reconstruction of the Jurassic conifer Sewardiodendron laxum (Taxodiaceae)

Compressed seed cones and pollen cones of Sewardiodendron laxum are described from the Middle Jurassic of Yima, Henan, central China. They are either organically attached to or associated with leafy shoots. Seed cones are terminally borne. Each cone is ovate to elongated, up to 6.5 cm long and 3.5 cm wide, and consists of a stout axis and numerous helically arranged bract-scale complexes. The bract protrudes beyond and is partially fused with the reduced ovuliferous scale. The ovuliferous scale bears approximately six inverted, small, and flattened seeds. Pollen cones are borne in terminal clusters. Microsporophylls are helically arranged, each bearing three abaxial, basally fused pollen sacs. Pollen is assaccate, rounded, and with an inconspicuous pore. Morphological, structural, and cuticular features of seed cones, pollen cones, and leafy shoots of S. laxum are compared with those of fossil and extant conifers. S. laxum is included in Taxodiaceae and believed to have its closest affinities with a Mesozoic conifer Elatides and a group of Cunninghamia-like conifers. It is reconstructed as a half-evergreen tree that lived in a humid, warm-temperate climate.     

Frenelopsis alata and its microsporangiate and ovuliferous reproductive structures from the Cenomanian of Bohemia (Czech Republic, Central Europe)

The conifer, Frenelopsis alata (K. Feistmantel) E. Knobloch (Cheirolepidiaceae), occurring mostly in the Cenomanian of Europe, is revised on the basis of the type material. Its comparison with relevant species of Frenelopsis is discussed.The ovuliferous cone associated with the genus Frenelopsis is recorded for the first time. For the associated ovuliferous cones of Frenelopsis, a new genus, Alvinia, is introduced in a new combination for the type: Alvinia bohemica (Velenovsky) comb. n. Its association with Frenelopsis alata is based on the presence of Classopollis pollen adhering to ovuliferous cone scales, and the same type of pollen found in the microsporangiate cone of F. alata, the same cuticle pattern present on ovuliferous cones, sterile twigs and microsporangiate cones of F. alata, and also the co-occurrence of ovuliferous cones or their scales and sterile twigs of F. alata.Large ovuliferous cones of Alvinia bohemica are formed by helically arranged ovuliferous scales subtended by bracts. Each ovuliferous cone scale displays one or two seeds covered by a covering flap, and three appendages, which form distally a funnel-like structure lined in its inner part by long trichomes. Numerous pollen grains of Classopollis adhere to the trichomes, and the structure is considered to function as a protostigmatic area.The ovuliferous cones of Alvinia differ from similar cones of the Cheirolepidiaceae, Hirmeriella and Tomaxellia, mainly in a high state of unification of the ovuliferous cone scale, reduction of appendages and in a presence of the protostigmatic funnel-like structure.The ovuliferous cones, Alvinia bohemica, rarely occur intact, so it is assumed that they disintegrate when mature. It seems likely that they were not woody. This assumption is supported by the flattened appearance of cones and their cone scales in the sediment, their flexibility and the absence of massive coaly matter known from cones of the Taxodiaceae and Cupressaceae. It is proposed that this type of ovuliferous cone scale indicates a specialized type of pollination. In addition, it is suggested that cone scales enclosing seeds play an important role in propagation.     

Morphological "primary homology" and expression of AG-subfamily MADS-box genes in pines, podocarps, and yews

The morphological variation among reproductive organs of extant gymnosperms is remarkable, especially among conifers. Several hypotheses concerning morphological homology between various conifer reproductive organs have been put forward, in particular in relation to the pine ovuliferous scale. Here, we use the expression patterns of orthologs of the ABC-model MADS-box gene AGAMOUS (AG) for testing morphological homology hypotheses related to organs of the conifer female cone. To this end, we first developed a tailored 3'RACE procedure that allows reliable amplification of partial sequences highly similar to gymnosperm-derived members of the AG-subfamily of MADS-box genes. Expression patterns of two novel conifer AG orthologs cloned with this procedure-namely PodAG and TgAG, obtained from the podocarp Podocarpus reichei and the yew Taxus globosa, respectively-are then further characterized in the morphologically divergent female cones of these species. The expression patterns of PodAG and TgAG are compared with those of DAL2, a previously discovered Picea abies (Pinaceae) AG ortholog. By treating the expression patterns of DAL2, PodAG, and TgAG as character states mapped onto currently accepted cladogram topologies, we suggest that the epimatium-that is, the podocarp female cone organ previously postulated as a "modified" ovuliferous scale-and the canonical Pinaceae ovuliferous scale can be legitimally conceptualized as "primary homologs." Character state mapping for TgAG suggests in turn that the aril of Taxaceae should be considered as a different type of organ. This work demonstrates how the interaction between developmental-genetic data and formal cladistic theory could fruitfully contribute to gymnosperm systematics.     

A new species of Masculostrobus Seward producing Classopollis pollen from the Jurassic of Iran

A male cone associated with Brachyphyllum expansum (Sternberg) is described from the Middle Jurassic of the Elburz Mountains in Northern Iran (Persia). The cone is described as M. rishra a new species of Masculostrobus Seward and the genus is emended to restrict its use for conifer male cones containing non-saccate pollen. M. rishra is compared with the cones occurring with B. expansum at the type locality of the latter in England. M. rishra contains pollen of the kind known as Classopollis torosus (Ressinger) sensu lat. and it is compared with the male cones of the Jurassic conifers, Cheirolepidium muensteri (Schenk), Brachyphyllum Scotti Kendall and Pagiophyllum connivens Kendall. The possibility that these conifers with similar male cones and pollen all belong to a single family, the Cheirolepidaceae, is suggested.     

Predation and protection in the macroevolutionary history of conifer cones

Conifers are an excellent group in which to explore how changing ecological interactions may have influenced the allocation of reproductive tissues in seed plants over long time scales, because of their extensive fossil record and their important role in terrestrial ecosystems since the Palaeozoic. Measurements of individual conifer pollen-producing and seed-producing cones from the Pennsylvanian to the Recent show that the relative amount of tissue invested in pollen cones has remained constant through time, while seed cones show a sharp increase in proportional tissue investment in the Jurassic that has continued to intensify to the present day. Since seed size in conifers has remained similar through time, this increase reflects greater investment in protective cone tissues such as robust, tightly packed scales. This shift in morphology and tissue allocation is broadly concurrent with the appearance of new vertebrate groups capable of browsing in tree canopies, as well as a diversification of insect-feeding strategies, suggesting that an important change in plant-animal interactions occurred over the Mesozoic that favoured an increase in seed cone protective tissues.     

A NEW SCIADOPITYACEOUS SEED CONE FROM THE UPPER CRETACEOUS OF HOKKAIDO,JAPAN

A sciadopityaceous seed cone, Sciadopityostrobus kerae, gen. et sp. nov., is described on the basis of a permineralized specimen from the Upper Cretaceous (Cenomanian–Coniacian) of Hokkaido, Japan. The peel method was applied for anatomical observations. The seed cone consists of a cone axis receiving numerous cone scale complexes that are arranged helically. Each complex generally has five inverted ovules that are oriented adaxially. The cone is similar to those of living Sciadopitys verticillata with respect to its peltate cone scale complex, with free apices of both bract and ovuliferous scale, trichomes on the bract, and a trifurcated ovuliferous scale strand. In the fossil, the bract and ovuliferous scale strands fuse with each other in the basal part of the cone scale complex, while S. verticillata bract and ovuliferous scale strands are derived separately from the vascular cylinder and remain separate throughout their length. The present specimen is one of the oldest records of structurally preserved cones that can be assigned to the family Sciadopityaceae.     

A taxodiaceous seed cone from the Triassic of Antarctica

A silicified seed cone is described from the lower Middle Triassic of A silicified seed cone is described from the lower Middle Triassic of Antarctica. The cone measures up to 3.4 cm long and 1.4 cm wide, and consists of helically arranged cone scales attached to a eustelic axis. Bract and ovuliferous scale are approximately of equal length and fused at the base. The bract is entire and vascularized by a single trace. The ovuliferous scale contains five distal lobes, each vascularized by a terete strand that divides to form a smaller trace to each of the five inverted ovules. Ovules are small and flattened with the three-parted integument attenuated into oppositely positioned lateral wings. The Triassic specimens are compared with both extant and fossil conifer seed cones and believed to have their closest affinities within the Taxodiaceae.     

Implications of fossil conifers for the phylogenetic relationships of living families

Fossils have played a central role in our understanding of the evolution of conifers. Interpretation of the seed cone as a compound strobilus and the homologies of the ovuliferous scales of modern conifers with the axillary dwarf shoot of Pennsylvanian forms are based on fossils. Similarly, early evolutionary trends involving the reduction, fusion, and planation of the fertile and sterile elements of the axillary dwarf shoot, leading to structures characteristic of modern families, are documented in Late Permian and Triassic conifers. However, a phylogeny elucidating the derivation of modern families from fossil forms based on shared derived features has been elusive. The present cladistic treatment using 11 characters of ovulate cones and one of pollen grains suggests three phylogenetic groups of Late Paleozoic conifers, represented loosely by the Emporicaceae, Utrechtiaceae, and Majonicaceae of Mapes and Rothwell. The Taxaceae appears to have diverged from ancestors within the Utrechtiaceae, whereas the other modern families owe their origins to the Majonicaceae. The origin of the Taxodiaceae appears to have been biphyletic.Taxodium, Cupressus andSciadopitys are strongly linked toDolmitia of the Majonicaceae, butCryptomeria, Cunninghamia andAraucaria are grouped together and diverge basal to the former taxa.Pinus branches from a position basal to the known genera of the Majonicaceae and all modern families except the Taxaceae.Podocarpus also diverges basal toMajonica but may share an ancestor with this genus;Cepahalotaxus diverges basal to theDolmitiaPseudovoltzia subclade but distal toMajonica. Similarly, the Cheirolepidiaceae originated from basal members of the Majonicaceae and shows no close phylogenetic relationship with any modern family. Except for a strong linkage betweenCycadocarpidium and theAraucariaCunninghamia subclade, genera of the Voltziaceae appear to have branched more or less independently from within the Majonicaceae and show no strong affinity with modern conifers. Thus differences between modern conifer families are due mainly to their divergence from different Paleozoic ancestors.     

Cone and ovule development in Cunninghamia and Taiwania (Cupressaceae sensu lato) and its significance for conifer evolution

We examined the early developmental stages of the seed cones and seeds of two conifer genera, Cunninghamia and Taiwania, using scanning electron microscope (SEM) images of freshly collected material. In recent similar studies, these two taxa were not described. The present paper aims to fill that gap. Both genera appear to have features crucial to the understanding of the evolution of the cupressaceous cone, characteristic of the families Cupressaceae and Taxodiaceae, and provide further evidence for the need to merge these families. These features are: the ovuliferous scale in Cunninghamia develops as a small lobe with each of three ovules; in Taiwania these lobes are absent, but a small ridge could be a vestige of them. In neither of these two genera does an ovuliferous scale develop to maturity and only limited intercalary growth transforms the bracts, of which only their width and final shape distinguishes them from sterile leaves. Thus, the bracts, not the ovuliferous scales, form the mature cone in these two genera. This trend is continued in more derived genera of Cupressaceae. Another key extant taxon that has helped to elucidate the evolution of this type of conifer cone is Sciadopitys; similar studies have already been done on this genus, and we compared our findings to them. We also considered certain fossil Mesozoic conifer cones, which shed further light on the evolution of the cupressaceous cone. The evidence from these various genera strongly indicates that recently reconstructed phylogenies of gymnosperms based on molecular evidence from extant taxa do not reflect the evolution that actually happened. Such studies need to take into account nonmolecular evidence, as detailed here.     

On a new specimen of Pseudoaraucaria major Fliche (Pinaceae) from the Cretaceous of the Isle of Wight

The well-preserved permineralized cone is identified chiefly on the basis of its large size and large seeds with a relatively thin sclerotesta. The detailed anatomy conforms to that characteristic of this highly distinctive and probably natural genus of early Pinaceae. The structure of the scale lends support to the theory that the partially embedded seeds escaped from the ripe cone by the bending back of the upper part of the scale. The specimen confirms that the seed testa typically possessed resin cavities as it does in certain living genera. The relationship of Pseudoaraucaria with other Pinaceae is discussed in the light of the results of a numerical analysis of 22 cone characters, lending support to the recent suggestion that Pseudoaraucaria may have occupied a central position in the early evolution of the family.     

The phylogenetic position of taxaceae based on 18S rRNA sequences

The evolutionary position of the yew family, Taxaceae, has been very controversial. Some plant taxonomists strongly advocate excluding Taxaceae from the conifer order and raising its taxonomic status to a new order or even class because of its absence of seed cones, contrary to the case in the majority of conifers. However, other authors believe that the Taxaceae are not fundamentally different from the rest of the conifers except in that they possess the most reduced solitary-ovule cones. To resolve the controversy, we have sequenced the 18S rRNA genes from representative gymnosperms: Taxus mairei (Taxaceae), Podocarpus nakaii (Podocarpaceae), Pinus luchuensis (Pinaceae), and Ginkgo biloba (Ginkgoales). Our phylogenetic analysis of the new sequence data with the published 18S rRNA sequence of Zamia pumila (a cycad) as an outgroup strongly indicates that Taxus, Pinus, and Podocarpus form a monophyletic group with the exclusion of Ginkgo and that Taxus is more closely related to Pinus than to Podocarpus. Therefore, Taxaceae should be classified as a family of Coniferales. Our finding that Taxaceae, Pinaceae, and Podocarpaceae form a clade contradicts both the view that the uniovulate seed of Taxaceae is a primitive character and the view that the Taxaceae are descendants of the Podocarpaceae. Rather, the uniovulate seed of Taxaceae and that of some species of Podocarpus appear to have different origins, probably all reduced from multiovulate cones. Correspondence to: W.-H. Li     

OVULE INVERSION IN THE EARLIEST CONIFERS

Recent investigations of ovulate conifer cones from southern Europe and midcontinent North America have independently documented that certain Paleozoic walchians have inverted ovules, rather than the erect ovules previously thought to characterize the most primitive conifers. Reinvestigation and consideration of other walchian conifers, including Moyliostrobus and Lebachia piniformis (sensu Florin), reveals that they also had inverted ovules. These different patterns of ovule orientation demonstrate that the nature and the polarity of the character states are dramatically different than popularly believed, and the shift from megasporophyll to ovuliferous cone-scale occurred within the Paleozoic walchians.     

Variation among individuals in cone production in Pinus palustris (Pinaceae)

? Premise of the study: Reproductive output varies considerably among individuals within plant populations, and this is especially so in cone production of conifers. While this variation can have substantial effects on populations, little is known about its magnitude or causes. ? Methods: We studied variation in cone production for 2 years within a population of Pinus palustris Mill. (longleaf pine; Pinaceae). Using hurdle models, we evaluated the importance of burn treatments, tree size (dbh), canopy status (open, dominant, subordinate), and number of conspecific neighbors within 4 m (N(4)). ? Key results: Cone production of individuals-even after accounting for other variables-was strongly correlated between years. Trees in plots burned every 1, 2, or 5 years produced more cones than those burned every 7 years, or unburned. Larger trees tend to produce more cones, but the large effects of the other factors studied caused substantial scatter in the dbh-cone number relationship. Among trees in the open, dbh had little explanatory power. Subordinate trees with three neighbors produced no cones. ? Conclusions: Tree size alone was a weak predictor of cone production. Interactions with neighbors play an important role in generating reproductive heterogeneity, and must be accounted for when relating cone production to size. The strong between-year correlation, together with the large variance in cone production among trees without neighbors, suggests that still more of the variance may be explainable, but requires factors outside of our study.