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: Hedyotis longifolia (Gaertn.) Hook.; Hedyotis longifolia (Gaertn.) Hook. var. tenuifolia (Nutt.) Torr. & Gray; Hedyotis purpurea (L.) Torr. & Gray var. longifolia (Gaertn.) Fosberg; Houstonia longifolia Gaertn. var. glabra Terrell; Houstonia longifolia Gaertn. var. tenuifolia (Nutt.) Wood; Houstonia tenuifolia Nutt.; Oldenlandia purpurea (L.) Gray var. tenuifolia (Nutt.) Gray ex Chapman.
Known Distribution in Maine: This rare plant has been documented from a total of 24 town(s) in the following county(ies): Cumberland, Kennebec, Penobscot, Piscataquis, Sagadahoc, Somerset.
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.