Definitions

bog aster

Oclemena

Oclemena E.L.Greene, is a small genus of flowering plants from the sunflower family (Asteraceae).

It is native to northeastern North America, found in wet or dry woodlands, and sometimes in clearings in the woods, or in acid bogs and peat.

The finely woolly stem grows in a zig-zag fashion to a height 30-100 cm (1 to 3 feet). It may be red at its base.

The lanceolate leaves are numerous, arranged in a spiral whorl around a single stem. They can be sharply toothed along the margin (as in O. acuminata) or smooth (as in O. nemoralis). The leaves contain sessile resin glands.

The flower heads consist of flat-topped pink to rose-violet ray florets and yellow disk florets. There are one to a few on a plant, growing on a slender peduncle. The disk flowers are abruptly expanded at the top. The scarious floral bracts consist of narrow chlorophyllous bands, tinted with purple along the midrib.

The stipitate ovaries are generally compressed and show on the surface minute, cylindrical glands. The fruit is a glandular achene with a double pappus of two bristled whorls.

The chromosome base number is x=9.

The Kew database Vascular Plant Families and Genera categorizes Oclamena under the genus Aster L. But taxonomically, Oclemena belongs to the North American clade of the tribe Astereae, as a basal member of one of the main branches (Brouillet, Allen, Semple and Ito 2001).

Species

  • Oclemena acuminata (Michx.) Greene : Whorled Wood Aster, Sharpleaf Aster, White Wood Aster
  • Oclemena × blakei (Porter) Nesom (O. acuminata × O. nemoralis) : Blake’s Aster
  • Oclemena nemoralis (Ait.) Greene : Bog Aster, Bog Nodding Aster.
  • Oclemena reticulata (Pursh) Nesom : Pinebarren Whitetop Aster.

References

  • SEMPLE, J.C., S. HEARD and CHUNSHENG XIANG. 1996. The Asters of Ontario (Compositae: Astereae): Diplactis Raf., Oclemena Greene, Doellingeria Nees and Aster L. (including Canadanthus Nesom, Symphyotrichum Nees and Virgulus Raf.)
  • SEMPLE, J.C., S.B. HEARD and L. BROUILLET. 2002. Cultivated and native asters of Ontario (Compositae: Astereae): Aster L. (including Asteromoea Blume, Diplactis Raf. and Kalimeris (Cass.) Cass.), Callistephus Cass., Galatella Cass., Doellingeria Nees, Oclemena E.L. Greene, Eurybia (Cass.) S.F. Gray, Canadanthus Nesom, and Symphyotrichum Nees (including Virgulus Raf.). U. Waterloo. Biol. Series No. 41: 1-134.

Category : Asteraceae

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