Smooth Ruellia, Limestone Petunia

Ruellia strepens

Family: Acanthaceae (ah-kanth-AY-see-ee) (Info)
Genus: Ruellia (roo-EL-ee-uh) (Info)
Species: strepens (STREP-enz) (Info)
Synonym:Dipteracanthus micranthus
Synonym:Dipteracanthus strepens



Foliage Color:

Unknown - Tell us

Bloom Characteristics:

This plant is attractive to bees, butterflies and/or birds

Water Requirements:

Average Water Needs; Water regularly; do not overwater

Where to Grow:

Unknown - Tell us


12-18 in. (30-45 cm)

18-24 in. (45-60 cm)

24-36 in. (60-90 cm)


15-18 in. (38-45 cm)


USDA Zone 5a: to -28.8 C (-20 F)

USDA Zone 5b: to -26.1 C (-15 F)

USDA Zone 6a: to -23.3 C (-10 F)

USDA Zone 6b: to -20.5 C (-5 F)

USDA Zone 7a: to -17.7 C (0 F)

USDA Zone 7b: to -14.9 C (5 F)

USDA Zone 8a: to -12.2 C (10 F)

USDA Zone 8b: to -9.4 C (15 F)

Sun Exposure:

Partial to Full Shade



Bloom Color:


Bloom Time:

Mid Summer

Late Summer/Early Fall



Other details:

Unknown - Tell us

Soil pH requirements:

6.1 to 6.5 (mildly acidic)

6.6 to 7.5 (neutral)

7.6 to 7.8 (mildly alkaline)

Patent Information:


Propagation Methods:

From seed; direct sow outdoors in fall

From seed; sow indoors before last frost

From seed; direct sow after last frost

Self-sows freely; deadhead if you do not want volunteer seedlings next season

Seed Collecting:

Allow pods to dry on plant; break open to collect seeds


This plant has been said to grow in the following regions:

Barling, Arkansas

Valparaiso, Indiana

Benton, Kentucky

Frenchtown, New Jersey

Bethlehem, Pennsylvania

San Augustine, Texas

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Gardeners' Notes:


On Jun 25, 2014, Clint07 from Bethlehem, PA wrote:

Short version: it's pretty and/but spreads by re-seeding.
The specific epithet "repens" means something like "noisy" for when the seed capsule explodes and broadcasts the seed. Young leaves have a sandpapery texture on the underside. Its roots are hard to get up.


On Apr 10, 2012, plant_it from Valparaiso, IN wrote:

Beautiful blue/purple flower. Also called Smooth Petunia, it's native to my state of Indiana. It's range extends south from Pennsylvania, Michigan, and Nebraska to Florida and Texas (NatureServe 2010). It's considered threatened in Michigan and Pennsylvania.

"Habitats include moist to mesic open woodlands, woodland edges, areas along woodland paths, thickets, and thinly wooded slopes along rivers. In woodlands where there is an absence of fire or other disturbance, the population of this plant may decline because of excessive shade, particularly when those woodlands have become dominated by Sugar Maple and various Honeysuckle shrubs."

Difficul... read more


On Jul 7, 2011, robinclark24 from Murfreesboro, TN wrote:

One word: invasive!

I bought from a small nursery what I thought was similar to cranesbill. Not so much. I don't think the birds have carried it but it is now nearly in every bed I have, including a front bed.

It didn't bloom the first year & bloomed a little this year. Not worth the work for me, for sure. Unfortunately, it breaks off of the root when trying to pull each one has to be dug up. I'm going to have to protect it's neighbors & try some round up on them. But if you want'll give it to you. Mine is/was 2.5-3' tall & in full sun.


On Jun 23, 2006, melody from Benton, KY (Zone 7a) wrote:

A cheerful little wildflower that seems perfectly at home in full sun or in light shade. Seems to tolerate a range of conditions and while there aren't always lots of blooms, it's dependable and cast iron here in west KY.

The ones I found were even growing up through needles underneath some very old pine trees.