摘要:

HUFFORD, L.D.&ENDRKSS, P. K., 1989.The diversity of anther structures and dehiscence patterns among Hamamelididae.This survey of anther structures and dehiscence patterns focuses on the range of diversity among extant Hamamelididae. The definition and structure of the anther stomium are considered in detail to provide a basis for characterizing dehiscence patterns. We are concerned particularly with the structural basis and distribution of so‐called valvate dehiscence, which we define here as occurring only in those anthers that possess stomial bifurcations or markedly eccentric stomia. Valvate dehiscence is restricted to Trochodendrales and Hamamelidales among Hamamelididae, although some Hamamelidaceae possess only linear, not markedly eccentric stomia that lead to longitudinal dehiscence patterns. Anther forms are somewhat variable and do not appear to be highly correlated with stomial patterns, although stomial bifurcations occur most frequently in anthers with broad, thick connectives that extend for the full length (or nearly so) of the thecae. Valvate dehiscence usually occurs in anthers in which the pollen sacs are embedded in bulky superficial tissues. An evolutionarily secondary extension of the stomium around the thecal shoulders seems to have occurred in taxa with a nonextensive connective and may facilitate a broader anther opening in cases of longitudinal dehiscence. An endothecial‐like connective hypodermis is a notable characteristic among examined ‘Lower Hamamelididae’ (exceptDisanthus)and is also present inDaphnipfiyllumandEucommia.We hypothesize that this specialized connective hypodermis facilitates a broader opening of the

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1989.tb00406.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

FISHER, J. B., GOH, C. J.&RAO, A. N., 1989.Non‐axillary branching in the palmsEugeissonaandOncosperma(Arecaceae).The south‐east Asian palms,Eugeissona(Calamoideae) andOncosperma(Arecoideae) are multiple‐stemmed. The morphology and development of branching in two species of each genus were examined in Singapore, Borneo, and the Malay Peninsula. Cultivated seedling and adult plants of0. tigillariumwere also observed in Florida. A new shoot arises most often from a longitudinal abaxial groove at the base of an enclosing leaf sheath. In some instances, especially inE. tristis, the enclosing leaf has two equal, adjacent grooves such that any distinction between an original mother shoot and a lateral daughter shoot is impossible. No axillary buds occur inEugeissonawhich is hapaxanthic. InOncosperma, which is pleonanthic, axillary buds are absent from young pre‐flowering stems, but an inflorescence bud occurs in the axil of each leaf in older aerial stems. Early ontogenetic stages of vegetative branching, as seen in sectioned apices, indicate that a new vegetative shoot is present on the abaxial base of the first (youngest) leaf primordium. There is no ontogenetic evidence for the displacement of an originally axillary meristem as previously described for the palmSalacca(Calamoideae). Shoot development inEugeissonais interpreted as a putative dichotomy of the apical meristem in which the meristem centres commonly develop unequally. InOncospermathe smaller sucker bud meristem may be described as an abaxial leaf base bud, but ontogenetic variations indicate this form of branching is close to dichotomous branching. These new examples of non‐axillary branching are compared to similar cases previously reported for palms and other monoc

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1989.tb00407.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

HUGHES, L.&RICHARDS, A. J., 1989.Isozymes and the status ofTaraxacum(Asteraceae) agamospecies.Genetic identities I and Similarity Indices SI are calculated between 12 samples ofTaraxacum, on the basis of 40 isozymes at 15 loci for 10 enzyme systems. Samples included three polyploid agamospermous populations from northern England (group 1), three sexual diploid populations from south‐central France (group 2), and six accessions of ‘primitive’ diploid self‐compatible sexual taxa from southern Europe and Australia. Samples could be assigned to eight species, classified in seven sections of the genus.Two clusters of high relationship were evident. All the group 1 and group 2 species were very closely related, with pairwise comparisons for I in excess of 0.93. The three group 3 accessions identified asT. bessarabicumshowed pairwise comparisons for SI in excess of 0.71. Comparisons for SI between the other group 3 species, and between all the group 3 species and the group 1 and 2 species were all very low, not exceeding 0.45.It is concluded that dissimilarity between samples as assessed by isozymes is probably related to the time of evolutionary divergence of those samples. Although allopolyploid, and morphologically very diverse, the group 1 agamospecies may have very recently diverged asexually from a common stock. The group 2 diploids may have resulted from rediploidization and regained sexuality from the same originally agamospermous stock. In areas of Europe in which such ‘modern’ sexuality is common, it is probable that all ‘modern’ Taraxaca, including at least five sections of the genus, should be included within a single taxon.In contrast, ‘primitive’ self‐compatible sexual species in group 3 appear to have diverged from each other several million years ago, and with the exception of the disjunct accessions ofT. bessarabicum, are genetically highly distinct. Such species should be maintained in the taxonomies of all areas. It is probable that an agamospecies classification of ‘modern’Taraxacumwill continue to convey much useful information in areas, such as northern Europe, in

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1989.tb00408.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SHEFFIELD, E., WOLF, P. G., HAUFLER, C. H., RANKER, T. A.&JERMY, A. C, 1989.Are‐evaluation of plants referred to asPteridiutn herediae(Colmeiro) Love&Kjellqvist.Based on perceived differences in morphology, chromosome number and habitat, specimens ofPteridiutnfrom southern Spain have been segregated by previous authors as a species distinct fromPteridium aquilinum, and calledPteridium herediae.However, type specimens of this taxon cannot be found. New collectionsof Pteridiumfrom similar habitats in the area were examined and analysed in the present study and the results compared with those from British plants(P. aquilinum).The Spanish plants were not found to differ significantly fromP. aquilinummorphologically, and all yielded chromosome counts (sporophytes, 104; gametophytes, 52) considered typical for the genus. Genotype frequency data obtained from isozyme electrophoresis of Spanish and BritishPteridiumyielded a genetic identity of 0.86; well within intraspecific distances found in other ferns.These data indicate that there are currently no grounds for accepting that a formof Pteridium, distinguishable fromP. aquilinumon the basis of differences in morphology, chromosome number, habitat or biochemistry, exists on the limestone soils of the Sierra de Cazorla region of southern Spai

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1989.tb00409.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

WILLMOT, A., 1989.The phenology of leaf life spans in woodland populations of the fernsDryopteris filix‐mas(L.) Schott andD. dilatata(Hoffm.) A. Gray in Derbyshire.The results of a survey on the number of upright fronds per plant in a population ofDryopteris filix‐masand in a population ofD. dilatataover a 14 month period are presented. These coupled with similar information on the number of developing fronds per plant demonstrate that large plants in the population of each species were summergreen, while small ones were wintergreen. This size‐specific difference in leaf phenology does not seem to have been recorded before inDryopteris filix‐mas.It is suggested that this difference, in both species, may have been due to either the different environments in which the plants grew or to a risk‐sensitive strategy in the small plants. It is considered that such a strategy might be concerned with the obtaining or retention of resources at a critical period in the life history of th

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1989.tb00410.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

VENTER, H.J. T.&FIELD, D. V., 1989.A new species ofStomatostemma(Periplocaceae) from Mozambique, Africa.A new species ofStomatostemmais described from Mozambique. 11 is [he second species distinguished in the genusStomatostemmaN.E. Br., the other beingS. monteiroae(Oliv.) N.E. Br., which was also described from Mozambique. The new species is distinguished from.V.monteiroaeby being a virgate shrub, by the pendulous terminal branches and inflorescences, by the long and frail peduncles and pedicels and by the long clavate corona lobes.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1989.tb00411.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

VENTER, H.J. T.&GILBERT, M. C, 1989.A new species ofRaphionacme(Periplocaceae) from north‐east Africa.A new species ofRaphionacmefrom north‐cast Africa is described. It is recognized by the puberulous lanceolate and wavy leaves, the purple corolla lobes, (he simple free filiform corona lobes, the massive laterally broadened stamina! filaments and the position of the gynoslcgium in the corolla mouth. The new species resemblesR. micheliide Wild, to a certain extent. Their coronas and stamens are alike in structure and implantation. However, they differ with regard to the corolla structure and the relative position of the gynostegium in the flower, and the length of the pedic

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1989.tb00412.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1989.tb00413.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY