Oclemena
Display parents3
Parent authorityG.L.Nesom
TaxonOclemena
AuthorityGreene[1]

Oclemena is a genus of flowering plants in the tribe Astereae within the family Asteraceae. All species in the genus are native to eastern North America. The species were originally included in the genus Aster so they are often referred to simply as asters. Since their flower heads are nodding in bud, they are sometimes called nodding-asters.

Description

Oclemena species are perennial, herbaceous plants that propagate via a swollen tuber at the tip of a slender, elongated rhizome. Stems are erect and unbranched, with dense long hairs. Stem leaves are sessile (or short-petiolate) and alternate. Leaf blades are sparsely dotted with short glandular hairs, each with a yellow to orange resin head. Leaf margins are either serrate (O. acuminata) or both entire and revolute. The inflorescence is either a single flower head (O. nemoralis) or a corymb of 2–46 flower heads on long, slender peduncles, nodding in bud (except O. reticulata). A flower head has 7–25 ray flowers, white or pink, and 14–35 disc flowers, pale or pinkish yellow, reddening at maturity. The chromosome base number is x=9.[2][3][4]

Oclemena acuminataOclemena nemoralisOclemena reticulata
Plant height10–80 cm tall5–70 cm tall30–90 cm tall
Number of leaves11–18
Clustered at the summit of the stem		30–100
Uniformly distributed along the stem		12–30
Uniformly distributed along the stem
Leaf blades10–45 mm wide1–8 mm wide10–40 mm wide
Leaf marginsProminently toothed with flat marginsEntire (or nearly so) and revoluteEntire (or toothed at the tip) and revolute
Flower heads5–461–159–40
Ray flowers15
White or tinged with pink		13–25
Pink to purple, seldom white		7–11
White to pink
Disc flowers14–3020–3515–30
HabitatForestsBogs, fens, mossy lake shoresSeasonally moist sandy places, bogs, wet pine flatwoods

The hybrid Oclemena × blakei is intermediate in appearance between its parents, Oclemena acuminata and Oclemena nemoralis.

Taxonomy

In 1903, the American botanist Edward Lee Greene established genus Oclemena by segregating two species, Aster acuminatus Michx. and Aster nemoralis Aiton.[2] Greene, initially drawn to this group of plants by the nodding habit of their flower heads in bud, had been using the name Oclemena acuminata on the labels of herbarium specimens since 1897. In 1995, the American botanist Guy L. Nesom segregated two additional taxa, Aster nemoralis var. blakei Porter and Aster reticulatus Pursh.[5] Nesom considered Oclemena to be monophyletic but closely related to Doellingeria Nees.[3] A major treatment of genus Oclemena appeared in Flora of North America in 2006:[4]

Scientific nameCommon nameYear describedYear publishedDistribution
Oclemena acuminata (Michx.) Greenewhorled wood aster18031903Eastern Canada, Eastern United States
Oclemena × blakei (Porter) G.L.Nesom
(O. acuminata × O. nemoralis)		Blake's aster18941995Eastern Canada, Northeastern United States
Oclemena nemoralis (Aiton) Greenebog aster17891903Eastern Canada, Northeastern United States
Oclemena reticulata (Pursh) G.L.Nesompinebarren whitetop aster18131995Southeastern United States

As of December 2025, the generic name Oclemena Greene is widely accepted.[6][7][8][9]

Oclemena belongs to the North American clade of the tribe Astereae, as a basal member of one of its main branches.[10]

Distribution and habitat

Oclemena species are native to eastern North America.[4][11] Oclemena acuminata is the most wide-ranging species, from the Appalachian Uplands of Newfoundland to the southern tip of the Appalachian Mountains in the U.S. state of Georgia. In contrast, Oclemena reticulata îs restricted to the extreme southeastern United States where other species of Oclemena are not found. Oclemena nemoralis and Oclemena × blakei are boreal species that prefer the cold acidic bogs of eastern Canada and northeastern United States.

References

  1. ^
  2. ^ Greene (1903).
  3. ^ Nesom (1995), pp. pp. 175–178.
  4. ^
  5. ^ Nesom (1995), p. 264.
  6. ^ "Oclemena Greene". 10230-1. Retrieved 10 December 2025.
  7. ^ "Oclemena Greene". WFO Plant List. Retrieved 4 December 2025.
  8. ^
  9. ^ "Oclemena Greene". Database of Canadian Vascular Plants. Retrieved 10 December 2025.
  10. ^ Brouillet, L., G.A. Allen, J.C. Semple, and M. Ito. 2001. ITS phylogeny of North American asters (Asteraceae: Astereae). Abstract. Botany 2001, August 2001. Albuquerque, N.M.
  11. ^

Bibliography

  • Britton, Nathaniel Lord & Brown, Addison (1913). An illustrated flora of the northern United States, Canada and the British possessions. 2nd ed. New York: Charles Scribner's Sons. Retrieved 13 December 2025.
  • Greene, Edward Lee (1903). "Further Segregates from Aster". Leaflets of Botanical Observation and Criticism. 1: 4–7. Retrieved 10 December 2025.
  • Nesom, Guy L. (1995). "Review of the taxonomy of Aster sensu lato (Asteraceae: Astereae), emphasizing the new world species". Phytologia. 77 (3): 141–297. Retrieved 10 December 2025.
  • 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.). University of Waterloo Biology Series No. 30: 1-88.
  • 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.). University of Waterloo Biology Series No. 41: 1-134.