The classification of dicotyledons: A study of the upper levels of the hierarchy

Abstract

Data on 83 attributes were compiled for a sample of 543 genera of dicotyledons. Computational analyses and subsequent consideration suggest that a useful distinction can be made between crassinucellate (mainly apetalous and polypetalous) and tenuinucellate (mainly sympetalous) genera. The crassinucellate series incorporates rather distinct caryophylloid and magnolioid assemblages, the former corresponding to a large extent with the Caryophyllidae of recent taxonomic schemes, the latter being a greatly extended version of the Magnoliidae. No evidence is found to support the Rosidae or Dilleniidae as taxonomic groupings. The tenuinucellate series seems to include two previously unrecognized major groups, here called acanthoids and asclepioids, plus Compositae and Umbelliferae as outliers. The large orders Rosales, Umbellales, and Myrtales may well be taxonomically unsound. The shortage and general inaccessibility of truly comparative data constitutes a serious difficulty in considering major taxonomic problems; in general these demand better information than seems currently obtainable if reliable results are to be obtained.

The host ranges, classification and identification of eight persistent aphid-transmitted viruses causing diseases in legumes

“…They represented less than one third of the papilionoid legume tribes (Polhill, 1981). There was no evidence that any of the isolates had a preference for test species within particular tribes, or for test species that represented particular sub-groups of the Crassinucelli and Tenuinucelli (Young and Watson, 1970), other than Leguminosae. This was confirmed by classifying the seed-lines by their virus responses.…”

The Relationships of Certain Tymoviruses Assessed from the Amino Acid Composition of Their Coat Proteins

“…Koenig and Givord [4] reported sero logical tests on the virions of a larger number of tymoviruses, showed that they fell into a linear series, and stated that this arrangement was not correlated with the geographical distribution of the viruses, nor with their host ranges, nor with the composition of the nucleic acid in their virions. Dale [5] disputed these conclusions and showed that Koenig and Givord's series was congruent with the earlier subdivision proposal and that, with two ex ceptions, the series was correlated with host range and base composition; all the viruses at the turnip yellow mosaic virus end of the series were first isolated from crassinucellate plants [6], and their virions contained nucleic acid with about 39 mol% of cytosine, whereas, with the exception of ononis yellow mosaic virus (OYMV), viruses from the Andean po tato latent virus end of the series came from tenuinucellate hosts and, with the exception of eggplant mosaic virus (EMV), their virions contained nucleic acids with cytosine contents around 34 mol%. In a recent, very compre hensive serological study of the virions of 13 members of the group, Koenig [7] has con firmed and extended her earlier studies, and shown that the relationships are best re presented in two dimensions by arranging the tymoviruses on a 'loop structure', which resembles the outline of a tennis racket.…”

Comparisons of the genomic sequences of erysimum latent virus and other tymoviruses: a search for the molecular basis of their host specificities

“…growing in East Germany. ELV, like turnip yellow mosaic virus (TYMV), causes diseases of wild and crop brassicas and preferentially infects (Guy et al, 1984) crassinucellate dicotyledonous plants (Young & Watson, 1970). However, despite these clear biological similarities to TYMV, its particles are serologically unrelated to those of TYMV and only distantly related to those of Andean potato latent (APLV) and ononis yellow mosaic (OYMV) tymoviruses .…”

“…These facts also indicate that the anomalous biological and serological relationships of ELV and TYMV do not result from genetic recombination of distantly related virion protein genes and Viral signals for host specificity Guy et al (1984) showed that tymoviruses preferentially infect species of the same family as their known natural host or hosts (e.g. Brassicaceae, Cucurbitaceae, Leguminosae, Sterculiaceae or Solanaceae), or of the same higher order grouping of dicotyledonous plants, that is the 'crassinucelli' or 'tenuinucelli' as defined by Young & Watson (1970). The aligned RPs and OPs of five tymoviruses, and a larger set of VPs, were searched for sequence similarities or motifs that might determine their host range preferences.…”