Vascular Plants of North Carolina
Account for Narrowleaf Bluet - Houstonia tenuifolia   Nuttall
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Members of Houstonia with account distribution info or public map:
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Section 6 » Family Rubiaceae
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DistributionScattered over the Piedmont and the mountains, but seemingly absent in the northern mountains, and large holes in parts of the Piedmont. Does not occur in the Coastal Plain.

This is a rather Southern species, ranging from PA to MO, south to SC and TX, barely to the FL Panhandle. Note that the BONAP map is incorrect, as it lumps this species into H. longifolia.
AbundanceUncommon as a whole in the Piedmont and mountains, but is locally fairly common in the northeastern Piedmont and again in the northwestern Piedmont, including the Brushy Mountains. It seems to be absent in the northern mountains and is locally quite scarce in parts of the Piedmont. As NatureServe does not consider it valid, even as a variety (!), the website editors have assigned a recommended Global Rank of G5.
HabitatThis species occurs in dry soil, typically over circumneutral soil, such as over gabbro, diabase, or amphibolite rock. It grows around the margins of flatrocks, granitic domes, in mafic glades and barrens, and in openings and borders of dry woodlands. The quite similar H. longifolia can grow in similar places but essentially over acidic soils.
PhenologyBlooms in June and July, and fruits shortly after flowering.
IdentificationThis is a quite slender species, branched a few times in the upper portions, and growing to about 8-10" tall. The pairs of opposite leaves are very narrowly linear, about 1" long but barely 1/10" wide at best. H. longifolia has narrow leaves that are oblong to narrowly elliptic, but are about 1/6-1/8" wide, noticeable in the field. The flower clusters are in cymes, with the numerous white to lavender-white flowers, similar to those of the other species, about 1/4" tall and 1/4" wide at the 4 spreading petals. This species has the flowers on noticeable stalks to about 2/5" long, whereas flowers in H. longifolia are nearly sessile (almost sitting on the upper leaves/bracts). Be careful separating these two, as both occur on dry soil and often near or around outcrops, though neither is rare.
Taxonomic CommentsMany references, including NatureServe, do not consider this as a valid species; even back as far as RAB (1968) and many others, it was considered a good species, as does Weakley (2018).

Other Common Name(s)Diffuse-branched Bluet
State RankS3 [S3S4]
Global RankGNR [G5]
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