摘要:

SummaryMany of the diverse floral characteristics used by taxonomists in assessing relationships among taxa represent adaptations to specific pollinators or pollinating methods. Therefore, the diversity of reproductive methods that occurs within a phylad has a strong influence on the number of taxa that are generally recognized in the phylad. Such evolutionary phenomena as convergence and adaptive radiation of floral patterns influence the taxonomic status of various phylads or the relationships that are seen among them. Incompatibility systems are generally unassociated with morphological distinctions, but are of practical importance in crossing programs designed to test the presence and nature of genetic isolation between species, since an unawareness of their existence may lead to erroneous taxonomic conclusions. Similarly, unilateral incompatibility is discussed in relation to certain practicalities in hybridization programs. Morphological features associated with dioecism and heterostyly are disscussed as a generally overlooked source of potentially very useful taxonomic characters. The importance of adaptations to different pollinators as a basis of interspecific isolating mechanisms is stressed, as are the possible positive evolutionary (and taxonomic) consequences of a breakdown in this isolation. Floral and other characters associated with autogamy are discussed and examples are given where the relationships of autogamous taxa are uncertain because of their highly specialized reduced flowers. It is suggested that taxonomists should make an attempt to understand the reproductive methods of the plants with which they work, since such an understanding will strengthen the foundation upon which taxonomic judgments are made.

ISSN:0040-0262    

DOI:10.2307/1218671

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryRecent developments in chemosystematics are reviewed with the conclusion that micro‐molecular data (essentially monomeric compounds such as flavonoids, alkaloids, terpenoids, amino acids, etc.) will prove most useful in resolving taxonomic problems at the generic level and lower while macromolecular data (polymeric compounds such as RNA, DNA, proteins, etc.) will prove most useful in resolvingphyleticproblems at the generic level and higher. Examples are given in which the two kinds of data have contributed to the resolution of such problems. Particular emphasis is placed upon the use of gas liquid chromatography in micro‐molecular studies, especially at the populational level. It is also concluded that protein‐band data and isoenzyme studies, as determined electrophoretically, because of the difficulty in establishing homology in the former and because of exceptional polymorphism in the latter, will be useful primarily at the specific level or lower. Developments have lagged in the application of serology and DNA hybridization to evolutionary problems in higher plant systematics and it appears that the most fruitful approach for unraveling phylogenetic pro. blems at the familial level or higher is that of animo‐acid sequence studies of metabolically important enzymes such as cytochrome c.

ISSN:0040-0262    

DOI:10.2307/1218672

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryThe extracellular metabolic end‐products that accumulate on the outer surface of the cell walls of the fungal hyphae in lichens have long been used in taxonomy. Although most morphological species of lichens are chemically uniform with regard to these substances, many others are differentiated into chemical races having distinct geographic distributions. The commonest type of chemical variation, noted in hundreds of examples, is a replacement series of the main constituent substances of the medulla. The fact that major chemical races in apparently sexually reproducing, morphologically uniform or nearly uniform lichens maintain their complete identity in places where they are sympatric suggests that such races are perhaps better regarded as distinct species. Such interpretation is further supported by the recent demonstration that where six such races are sympatric in an environmentally telescoped maritime community in Britain, the chemically different plants select different habitats, resulting in conspicuous zonation but with no alteration of plant characteristics where zones overlap. Examples of the use of lichen chemistry in genus‐level taxonomy are also given.

ISSN:0040-0262    

DOI:10.2307/1218673

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryThe first serious flora written in America (Thomas Walter'sFlora Caroliniana, 1788) was essentially a local flora, written by a plantation owner. Many subsequent early botanists were diverted away from local floras by the need of a general work (Thomas Nuttall, Amos Eaton, John Torrey, Asa Gray), but important local ones were also written (W. P. C. Barton, Jacob Bigelow, William Darlington). A majority of early botanists were Doctors of Medicine; smaller numbers were teachers, or belonged to other professions (e.g. Stephen Elliott, banker). Tabulation of state and local floras listed in Jackson'sGuide to the Literature of Botany(1881) and Blake and Atwood'sGeographical Guide to Floras of the World, Part I(1942), and of works published since the 1939 closing date for entries in the latter, shows that more and better ones are being produced in mid 20th Century than ever before in American history, but coverage of the country is still very incomplete and uneven. Despite current dominance of non‐floristic approaches to systematics, of other fields than systematics within botany, and of physical sciences over botany itself, the immediate future is likely to see continuation of the trend to more and better floras. The possible future history of local floras will end only if the entire human race is transported into outer space. General cultural conditions, economic factors, and world political problems will be important influences, but the surprising vigor of theanima naturaliter botanicain the face of difficulties in recent decades augurs very well for its future.

ISSN:0040-0262    

DOI:10.2307/1218674

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryIf the taxonomic system is to reflect the totality of similarities and differences among organisms, it must have an evolutionary foundation. Too rigid an adherence to the rule of monophylesis, however, would wreak havoc with our system. Similarities due to evolutionary parallelism provide some evidence of relationship, because the greater the genetic and phenetic similarity between two groups, the greater the likelihood that they will produce similar mutations, have similar evolutionary potentialities, and undergo parallel evolutionary change. A workable taxonomic system can provide only a muddy reflection of phylogeny.If the evolutionary diversification of any large taxonomic group were profoundly influenced by the nature of the supply of mutations, if the supply of mutations differed in the various subgroups, if the fixation of many of these mutations did not depend wholly on survival value, and if the evolutionary barriers between different ecologic niches or adaptive zones were in general low, then we might expect that group to show ecological and adaptive correlations most commonly at the lower taxonomic levels such as genera and species, whereas the higher taxa would tend to embrace a wide array of ecological types. These ecologically varied higher taxa would tend to be characterized in large part by features of doubtful adaptive significance, and the critical taxonomic characters for many of them would be so beset by exceptions that the recognition, characterization, and definition of the groups would often be difficult. The taxonomic pattern of the angiosperms, especially the dicotyledons, is precisely that which would be expected under the foregoing set of postulates.

ISSN:0040-0262    

DOI:10.2307/1218675

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryThe angiosperms are treated as a division Magnoliophyta, with two classes, the Magnoliatae (dicotyledons) and Liliatae (monocotyledons). Takhtajan's six subclasses of Magnoliatae are accepted with only minor alteration. These are the Magnoliidae, Hamamelidae, Caryophyllidae, Dilleniidae, Rosidae, and Asteridae. His four subclasses of Liliatae—the Alismatidae, Arecidae, Commelinidae, and Liliidae—are also accepted, but with a major transfer of the Zingiberales, Bromeliales, Juncales, and Cyperaceae from the Liliidae to the Commelinidae. The aquatic ancestry of the Liliatae has had a profound influence on the subsequent evolutionary history of the group. Loss of cambium, loss of vessels (except for some vestiges in the root), and reduction of the leaf to a phyllode are all probably associated with the ancestral aquatic habitat. The fact that habitai differences are often taxonomically more important among the monocots than they usually are among the dicots reflects the evolutionary difficul. ties under which monocots labor. The single cotyledon of monocots is considered to have arisen by lateral fusion of two, followed by reduction of one of the lobes, and the sheath‐blade structure of the leaves is considered to reflect the cotyledonary structure.

ISSN:0040-0262    

DOI:10.2307/1218676

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummarySince the precise origins of a type or critical collection and its subsequent history at the hands of persons who have annotated a specimen are critical in making taxonomic decisions, closer attention must be made to historical problems. Suggestions are offered apropos of four problems: (1) locating the literature, (2) locating the type, (3) establishing the type‐locality as precisely as possible, and (4) deciphering handwritings on labels.Library details include the (a) need to verify dates of issue, (b) need to check translations which may provide valuable annotations and supplement the original, (c) need to search for ancillary materials which may be nursery catalogues or other ephemera: these may help fix the date of a discovery or give other taxonomic history.In the search for the type the life and travels of an author may be important. An author like A. A. Heller who kept a personal herbarium, but who moved from city to city, or an author like A. W. Chapman who assembled two or more herbaria, each destined to lodge in a different institution, presents special problems. Destruction of a type necessitates the search for an isotype. This search should not be forsaken without a thorough canvass of collections which may contain an isotype.Precision in fixing a type locality may be lost when insufficient attention is paid to the collector's travels. Endemic taxa, for example, restricted to certain soils, or to particular geographic features may be involved. Travel narratives of other members of an expedition may also elucidate obscure place names which are possibly wanting on modern maps. Sequences of collector's numbers may or may not be significant in tracing routes since one must consider the possibility of mixed collection numbers.Handwriting is an important consideration, and there are several guides kept by prominent herbaria, and some maintain sample files. The practice of copying collection labels with each exchange of a specimen often has involved miscopying or abbreviating the original information, and so presents a common source of erroneous records. It must be recognized that handwriting modifies during the lifetime of the collector, and this necessitates checking against letters or contemporary holographic records. Fallacious and inaccurate conclusions may follow hasty research.

ISSN:0040-0262    

DOI:10.2307/1218677

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryIn response to skeptics who feel that the contribution of paleobotany to phylogeny is minimal, I have presented a number of examples where the fossil plant record has played an important role in demonstrating origins and relationships of various plant groups. Work on Precambrian thallophytes is one area where knowledge of earliest plant forms is taking on a definite form. New finds on the origin and evolution of Devonian land plants are presenting a clearer picture of early vascular plant evolution. Existence of such plants as the Progymnospermopsida has made it possible to understand the steps leading to the origin of gymnosperms. We now have important new knowledge concerning the evolution of the seed habit, as well as subsequent seed plant evolution. These are but a few examples of the contribution of paleobotany to phylogeny. This increasing sophistication in understanding phylogenetic events is indispensible for a system of plant classification that reflects relationships. Such a system of classification, I maintain, is much more meaningful than any other.

ISSN:0040-0262    

DOI:10.2307/1218678

出版商:Wiley    

年代:2019

数据来源: WILEY

ISSN:0040-0262    

DOI:10.1002/j.1996-8175.1969.tb02323.x

出版商:Wiley    

年代:2019

数据来源: WILEY

ISSN:0040-0262    

DOI:10.2307/1218680

出版商:Wiley    

年代:2019

数据来源: WILEY