Houstonia longifolia Gaertn.
Habitat: Slaty ledges or rivershore gravels, not strongly acidic. [Non-tidal rivershore (non-forested, seasonally wet)].
Range: Maine to Saskatchewan, south to Georgia, Oklahoma.
Aids to Identification: Bluets are small, slender plants with opposite stem leaves, small 4-petaled flowers, and inferior ovaries. The common bluet, Houstonia caerulea, found growing on lawns, has flowers that have a yellow center and horizontally spreading corolla lobes. Houstania longifolia has uniform colored white to pale blue flowers and ascending corolla lobes and occurs in different habitats.
Ecological characteristics: Usually found growing in slight cracks or depressions on rivershore ledges. Maine populations although apparently persistent are not large and the plants tend to be small.
Phenology: Herbaceous perennial, flowers July - September.
Synonyms: Formerly known as Hedyotis longifolia (Gaertn.) Hook., Houstonia purpurea var. tenuifolia (Nutt.) Gray.
Known Distribution in Maine: This rare plant has been documented from a total of 18 town(s) in the following county(ies): Cumberland, Kennebec, Penobscot, Sagadahoc, Somerset.
Dates of documented observations are: 1885, 18XX, 1906 (2), 1909, 1916, 1979, 1984 (2), 1986 (3), 1987 (3), 1988, 1989, 1990 (2), 1994, 1996 (3), 1997, 2000 (4), 2001, 2002
Reason(s) for rarity: Habitat naturally scarce, at northern limit of range.
Conservation considerations: Known populations are small, but the plant seems to persist on the few river ledges where it grows. Heavy recreational use of ledges could pose problems.