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Houstonia caerulea (Azure bluet)
Muller, Thomas L.

Houstonia caerulea

Houstonia caerulea L.

Azure Bluet, Quaker Ladies, Bluets

Rubiaceae (Madder Family)

Synonym(s): Hedyotis caerulea, Houstonia caerulea var. faxonorum

USDA Symbol: HOCA4

USDA Native Status: L48 (N), CAN (N), SPM (I)

This small, delicate perennial is found growing in compact tufts, 8 in. high. The plants may cover broad expanses. Tiny flowers are pale blue with yellow centers, tubular, four-lobed, solitary, and terminal. Spatula-shaped leaves occur in basal rosettes. Stem leaves are small and the stems are unbranched.

This lovely, delicate, flowering plant is often found in striking patches of light blue. The Star Violet (H. pusilla), to 4" (10 cm) high, has a tiny purple flower and occurs in fields and open woods from South Dakota east to Maryland and south to Florida and Texas. A tall southern species, 6-16" (15-40 cm) high, Large Houstonia (H. purpurea), has 3-5, ribbed, opposite, ovate leaves, and white or pink flowers. It occurs from Nebraska northeast to Maine and south to Florida and Texas. These and certain other Houstonia species have sometimes been placed in the genus Hedyotis.


From the Image Gallery

10 photo(s) available in the Image Gallery

Plant Characteristics

Duration: Perennial
Habit: Herb
Leaf Complexity: Simple
Fruit Type: Capsule
Size Notes: Up to about 8 inches tall.

Bloom Information

Bloom Color: Yellow , Blue
Bloom Time: Apr , May , Jun , Jul , Aug


USA: AL , AR , CT , DC , DE , GA , IL , IN , KY , LA , MA , MD , ME , MI , MO , MS , NC , NH , NJ , NY , OH , PA , RI , SC , TN , VA , VT , WI , WV
Canada: NB , NS , ON , QC
Native Distribution: N.S. to Ont. & WI, s. to GA, LA & AR; more common eastward
Native Habitat: Deciduous woods; moist meadows; clearings

Growing Conditions

Light Requirement: Part Shade
Soil Moisture: Moist
Soil pH: Acidic (pH<6.8)
Soil Description: Moist soils.
Conditions Comments: Bluets do well when grown among grasses of lawns and fields, but care should be taken not to mow them before they have set seed. Bluets are sometimes planted as a delicate, attractive addition to rock gardens.


Conspicuous Flowers: yes


Description: Plant seeds outside as soon as ripe or store, stratify and sow in the spring. Seeds should be sown at a shallow depth. These seedlings will germinate the first year and flower the second. Propagation by division is accomplished by digging the plants in
Seed Collection: Approximate collection date in northern U.S.: Late Jun. to mid Jul.
Seed Treatment: Moist stratification.
Commercially Avail: yes

National Wetland Indicator Status

This information is derived from the U.S. Army Corps of Engineers National Wetland Plant List, Version 3.1 (Lichvar, R.W. 2013. The National Wetland Plant List: 2013 wetland ratings. Phytoneuron 2013-49: 1-241). Click here for map of regions.

From the National Organizations Directory

According to the species list provided by Affiliate Organizations, this plant is on display at the following locations:

Delaware Nature Society - Hockessin, DE
Longwood Gardens - Kennett Square, PA
Mt. Cuba Center - Hockessin, DE

Web Reference

Webref 23 - Southwest Environmental Information Network (2009) SEINet - Arizona Chapter

Additional resources

USDA: Find Houstonia caerulea in USDA Plants
FNA: Find Houstonia caerulea in the Flora of North America (if available)
Google: Search Google for Houstonia caerulea


Record Modified: 2023-02-14
Research By: TWC Staff

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