The segregation of Packera from Senecio (Asteraceae)
Senecio, a group of largely yellow- to orange-flowered composites, have traditionally been broadly circumscribed. Recent research by Bremer (1994), Barkley (1999), and others, shows that the genus Senecio has included two separate lineages, each of which including multiple genera. One of these lineages, referred to as the Senecionoid Group, contains taxa for which nomenclatural changes have occurred affecting New England taxonomy. Note that these changes will be incorporated in the upcoming Flora of North America (volumes 19–21).
As to New England species, the genera of the Senecionoid Group can be distinguished by macromorphological features as follows:
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1a. Plants perennial with rhizomes and fibrous roots; leaves basally disposed (i.e., prominent clusters of basal leaves present, the stem leaves rapidly reduced in size upwards; Figure 1) ............................................................................................................................ Packera |
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1b. Plants annual or biennial (rarely short-lived perennial), mostly with evident taproots; leaves chiefly cauline (i.e., prominent clusters of basal leaves absent, the stem leaves gradually, if at all, reduced upwards; Figure 1) .................................................................................. Senecio |
Figure 1. General above ground habit of Packera and Senecio in New England. A—Packera aurea. B—Senecio vulgaris. Note distribution and size of leaves.
These genera (Packera and Senecio) are further distinguished by base chromosome number and pollen type (Barkley 1999).
Following is a checklist of the genus Packera in New England.
Packera aurea (L.) A. & D. Löve
Packera obovata (Muhl. ex Willd.) W.A. Weber & A. Löve
Packera paupercula (Michx.) W.A. Weber & A. Löve
Packera schweinitziana (Nutt.) W.A. Weber & A. Löve
The remaining species of New England ragworts are maintained in Senecio.
Literature Cited
Barkley, T. 1999. The segregates of Senecio, s.l., and Cacalia, s.l., in the flora of North America north of Mexico. Sida 18: 661–672.
Bremer, K. 1994. Asteraceae: Cladistics and Classification. Timber Press, Portland, OR.