Shared Character States Research Articles

New coniferophyte ovulate structures from the Early Permian of China

Recent research on the Cathaysian flora of the Early Permian Shanxi Formation in Henan Province, southern China has led to the identification of a new kind of fertile shoot system of spermatophyte affinity,Loroderma henaniagen.etsp. nov.From its morphological arrangement it is evident that this structure shares many similarities with known fossil coniferophyte taxa, although this particular combination of characters is unique, leading to the creation of a new genus and species. The fertile shoot system possesses a primary axis with helically arranged bract/shoot complexes, each consisting of a single lanceolate bract with parallel venation (indistinguishable fromCordaitessp. andRufloriasp.) with an ovulate cone in its axil. Ovulate cones consist of an elongate and recurved axis which in approximately its distal half bears scales and ovulate sporophylls. Each ovulate cone bears 1–3 ovules of theCardiocarpusorgan genus within the confines of the cone, although the precise nature of their attachment is unclear. The presence of shared character states with various extinct taxa has made it difficult to assign it unambiguously to any existing coniferophyte order or family as they are currently envisaged, with most likely affinities with or intermediate to the Vojnovskyales and Coniferales.

New coniferophyte ovulate structures from the Early Permian of China

Recent research on the Cathaysian flora of the Early Permian Shanxi Formation in Henan Province, southern China has led to the identification of a new kind of fertile shoot system of spermatophyte affinity,Loroderma henaniagen.etsp. nov.From its morphological arrangement it is evident that this structure shares many similarities with known fossil coniferophyte taxa, although this particular combination of characters is unique, leading to the creation of a new genus and species. The fertile shoot system possesses a primary axis with helically arranged bract/shoot complexes, each consisting of a single lanceolate bract with parallel venation (indistinguishable fromCordaitessp. andRufloriasp.) with an ovulate cone in its axil. Ovulate cones consist of an elongate and recurved axis which in approximately its distal half bears scales and ovulate sporophylls. Each ovulate cone bears 1–3 ovules of theCardiocarpusorgan genus within the confines of the cone, although the precise nature of their attachment is unclear. The presence of shared character states with various extinct taxa has made it difficult to assign it unambiguously to any existing coniferophyte order or family as they are currently envisaged, with most likely affinities with or intermediate to the Vojnovskyales and Coniferales.

Floral ontogeny ofZippelia begoniaefoliaand its familial affinity: Saururaceae or Piperaceae?

Zippelia begoniaefolia Bl., a monotypic species having characteristics of both Piperaceae and Saururaceae, has racemes of about 20 small flowers lacking a perianth, each with six free stamens and a four‐carpellate syncarpous gynoecium. The inflorescence apical meristem initiates bracts acropetally and helically, each of which subtends a later initiated single floral apex; there are no “common” primordia. The six stamens are initiated as two lateral pairs and two solitary successive primordia, the latter two opposite in median sagittal positions. Four carpel primordia are initiated as a lateral pair and two successively initiated in the median sagittal plane. This order of organ inception is unique among Piperaceae and Saururaceae. Intercalary growth below carpellary attachment raises them up on a common cylindrical base that becomes the syncarpous ovary, covered with unique glochidiate hairs and containing a single basal ovule. The free portions of the carpels become the reflexed papillate stigmas. The floral vascular system has a single bundle at base that branches to supply the bract and flower traces. The floral vasculature is similar but not identical to that of Saururus (Saururaceae) and some Piper species (Piperaceae). Plesiomorphic character states of Zippelia that are shared with Saururus include hypogyny, free stamens, cleft stigma, and a similar floral groundplan. Synapomorphies, derived shared character states that unite Zippelia with Piperaceae, include syncarpy, solitary ovule, basal placentation, fused ventral carpellary bundles, and a double vascular cylinder in the stem. Cladistic analysis aligns Zippelia with Piperaceae because they share apomorphies, and because Zippelia shares only plesiomorphies with Saururus.

Floral Ontogeny of Zippelia begoniaefolia and its Familial Affinity: Saururaceae or Piperaceae?

Zippelia begoniaefolia Bl., a monotypic species having characteristics of both Piperaceae and Saururaceae, has racemes of about 20 small flowers lacking a perianth, each with six free stamens and a four-carpellate syncarpous gynoecium. The inflorescence apical meristem initiates bracts acropetally and helically, each of which subtends a later initiated single floral apex; there are no “common” primordia. The six stamens are initiated as two lateral pairs and two solitary successive primordia, the latter two opposite in median sagittal positions. Four carpel primordia are initiated as a lateral pair and two successively initiated in the median sagittal plane. This order of organ inception is unique among Piperaceae and Saururaceae. Intercalary growth below carpellary attachment raises them up on a common cylindrical base that becomes the syncarpous ovary, covered with unique glochidiate hairs and containing a single basal ovule. The free portions of the carpels become the reflexed papillate stigmas. The floral vascular system has a single bundle at base that branches to supply the bract and flower traces. The floral vasculature is similar but not identical to that of Saururus (Saururaceae) and some Piper species (Piperaceae). Plesiomorphic character states of Zippelia that are shared with Saururus include hypogyny, free stamens, cleft stigma, and a similar floral groundplan. Synapomorphies, derived shared character states that unite Zippelia with Piperaceae, include syncarpy, solitary ovule, basal placentation, fused ventral carpellary bundles, and a double vascular cylinder in the stem. Cladistic analysis aligns Zippelia with Piperaceae because they share apomorphies, and because Zippelia shares only plesiomorphies with Saururus.

CYTOLOGICAL STUDIES IN LACCARIA (AGARICALES). II. ASSESSING PHYLOGENETIC RELATIONSHIPS AMONG LACCARIA, HYDNANGIUM, AND OTHER AGARICALES

Laccaria and Hydnangium typically undergo a postmeiotic mitotic nuclear division in basidiospores, basidia, or less commonly, in sterigmata resulting in eight nuclei. Basidiospores formed on tetrasterigmate basidia are binucleate, and those on bisterigmate basidia are tetranucleate in both genera. While Hydnangium and Laccaria likely comprise a monophyletic group-a hypothesis based on a number of shared characters-the presence of multinucleate basidiospores in several putative outgroups precludes using this shared character state as a justification for recognizing these two genera in a separate family, Hydnangiaceae, as had been proposed. Based on a review of the literature, the presence and location of postmeiotic mitotic divisions in basidia and basidiospores of Agaricales do not appear to be appropriate for assessing phylogenetic relationships among genera or families because of a high level of homoplasy.

COULD A CLADOGRAM THIS SHORT HAVE ARISEN BY CHANCE ALONE?: ON PERMUTATION TESTS FOR CLADISTIC STRUCTURE

Abstract Absolute criteria for evaluating cladistic analyses are useful, not only because cladistic algorithms impose structure, but also because applications of cladistic results demand some assessment of the degree of corroboration of the cladogram. Here, a means of quantitative evaluation is presented based on tree length. The length of the most‐parsimonious tree reflects the degree to which the observed characters co‐vary such that a single tree topology can explain shared character states among the taxa. This “cladistic covariation” can be quantified by comparing the length of the most parsimonious tree for the observed data set to that found for data sets with random covariation of characters. A random data set is defined as one in which the original number of characters and their character states are maintained, but for each character, the states are randomly reassigned to the taxa. The cladistic permutation tail probability, PTP, is defined as the estimate of the proportion of times that a tree can be found as short or shorter than the original tree. Significant cladistic covariation exists if the PTP is less than a prescribed value, for example, 0.05. In case studies based on molecular and morphological data sets, application of the PTP shows that: In the comparison of four different molecular data sets for orders of mammals, the sequence data set for alpha hemoglobin does not have significant cladistic covariation, while that for alpha crystallin is highly significant. However, when each data set was reduced to the 11 common taxa in order to standardize comparison, reduced levels of cladistic covariation, with no clear superiority of the alpha crystallin data, were found. Morphological data for these 11 taxa had a highly significant PTP, producing a tree roughly congruent with those for the three molecular sets with marginal or significant PTP values. Merging of all data sets, with the exclusion of the poorly structured alpha hemoglobin data, produced a data set with a significant PTP, and provides an estimate of the phylogenetic relationships among these 11 orders of mammals. In an analysis of lactalbumin and lysozyme DNA sequence data for four taxa, purine‐pyrimidine coding yields a data set with significant cladistic covariation, while other codings fail. The data for codon position 3 taken alone exhibit the strongest cladistic covariation. A data set based on flavonoids in taxa of Polygonum initially yields a significant PTP; however, deletion of identically scored taxa leaves no significant cladistic covariation. For mitochondrial DNA data on population genome types for four species of the crested newt, there is significant cladistic covariation for the set of all genome types, and among the five mtDNA genome types within one of the species. However, a conditional PTP test that assumes species monophyly shows that no significant cladistic covariation exists among the fur species for these data. In an application of the test to a group of freshwater insects, as preliminary to biological monitoring, individual subsets of the taxonomic data representing larval, pupal, and adult stages had non‐significant PTPs, while the complete data set showed significant cladistic structure.

The Stochastic Mode of Molecular Evolution: What Consequences for Systematic Investigations?

Abstract Biochemical characters have been proposed as ideal sources of phylogenetic information. The homologous characters are easily identified, the relationships between such characters and the underlying genetic code is well understood, and, most importantly, biochemical characters are thought to evolve in a stochastic, clock-like manner. I present a modified version of the Zuckerkandl and Pauling (1965) model of stochastic evolution which is used to explore the consequences of a stochastic mode of evolution. The probability of observing shared character states is determined as a function of the evolutionary rate of a character, the time of independent ancestry for two sister taxa, the time of shared ancestry for the sister taxa independent of their next closest relative, and the number of functionally equivalent, equally probable character states. I found that, while many branching patterns can be reliably reconstructed using stochastically evolving characters, a large subset of theoretically possible phylogenies (as defined by the duration of shared and independent ancestry) would not be derived correctly. The model simulates a "best-case scenario" in which the rate of character evolution is constant over time. Violation of this assumption complicates phylogeny reconstruction and further limits the types of phylogenies that can be addressed with stochastically evolving characters. I discuss the implications of these findings for data analysis and experimental design.

FUNCTIONAL ASPECTS OF THE EVOLUTION OF FROG TONGUES.

Amphibians are remarkable in having a that is propelled from the mouth, to impact on, adhere to, and pull prey into the buccal cavity. Although sometimes listed as a characteristic defining the class, it is only among certain salamanders and frogs that the appears to be flipped out rather than moved by incremental control. Its action is thus analogous to that of the projectile of chameleons (Gnanamuthu, 1930; Gans, 1967), rather than to the merely extensible of anteaters, some birds, and snakes. The mechanism of the of frogs, which is propelled by the rotation of soft tissues about the mandibular symphysis, is fundamentally distinct from that of the of salamanders, which is hurled anteriorly by a forward shift of the hyobranchial skeleton (Regal, 1966; Ozeti and Wake, 1969; Lombard and Wake, 1976; Larson and Guthrie, 1976). The has been used in the 19th Century and through the as a in the classification of frogs (cf. Lynch, 1973). However, the structure, function and evolution of this complex lingual system has received but minimal attention. Perhaps symptomatic of such neglect is that an obscure but beautiful study of the ontogeny and morphology of the and its intrinsic muscles in 42 species of frogs (MagimelPelonnier, 1924) has not been brought to light in any subsequent treatise on the frogs (Noble, 1931; Werner, 1930; Reeder, 1964; Blair, 1972; Vial, 1973) and, indeed, in the major handbook of vertebrate anatomy (Nishi, 1938). The mechanical basis of projection has long been discussed and debated, mainly for the advanced genera Rana and Bufo (Duges, 1827, 1835; Hartog, 1901; Gaupp, 1901; Barclay, 1942; Gnanamuthu, 1933; Boiker, 1937). Recently its mechanism has been explained anew (Tatarinov, 1951; Gans, 1961, 1962), though experimental confirmation is still lacking. It is commonly assumed that the condition of Rana or Bufo can be generalized at least for anurans belonging to nonarchaic or modern taxonomic groups, such as the Ranidae, Bufonidae, Hylidae, Leptodactylidae, and Rhacophoridae, in which the is attached in front with a flap posteriorly. The archaic taxonomic groups, the Ascaphidae (here both Liopelma and Ascaphus but see Savage, 1973), Discoglossidae, Pipidae, and Rhinophrynidae, are supposed to differ, having noneversile, posteriorly attached, or even completely margined tongues when present. The function of such tongues remains unstudied. We propose here that statements such as tongue present or tongue absent and even tongue with free flap posteriorly, do not necessarily define shared character states, but conceal critical biomechanical complexity and evolutionary parallelisms. It is not our intention here to a comprehensive monograph on frog structure and function. We document (1)