A taxanomic study of compositae with special reference to Senecio

Abstract

Senecio is the largest angiosperm genus, taking in about 1/7 of all Compositae and exhibiting nearly the whole range of vegetative diversity encompassed by the family. There is satisfactory definition of the genus, and the oft-quoted 'diagnostic' features are commonly lacking, especially among extra-european species. In fact, in the Genera PIantarum of Bentham and Hooker, the diagnosis of Senecio is essentially the same as that of the tribe Senecionideae. It is a commentary on taxonomic progress that the only comprehensive account is that of De Candolle (1837), although since his time the number of named Senecio species has increased fourfold. Clearly a reappraisal of the taxonomy of Senecio and of its relationships with other Compositae is long overdue.

Regarding the classification of Compositae, one finds that despite nama changes the tribes have altered very little since their delimitation and establishment by Cassini (1816-34). This is remarkable because the largest angiosperm family, taking in about 1/10 of the flowering plants, would seem to provide plenty of scope for discordant taxonomic opinion. Nevertheless Table 1 shows that of the 13 tribes recognised by Bentham (I873A), seven (i.e. 2, 3, 6, 7, 9, 10 and I3) are identical with or practically the same as Cassini's; and four (i.e. 5, 8, 11 and 12) incorporate or are merely fusion products of short sequences of Cassini's tribes with his groups adopted as subtribes. Only 2 of Cassini's tribes (i.e. 12 and 20) had suffered significant changes.

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