Thursday, December 22, 2011

Wild Petunia - Ruellia caroliniensis

Wild petunia (Ruellia caroliniensis) is a very common wildflower in Florida; found statewide in a variety of habitat types.  It is also distributed throughout the eastern half of North America, though it becomes much more rare in states such as Pennsylvania and New Jersey.  Wild petunia extends its range in the south as far west as Texas.
Though its flowers closely resemble those of the common garden petunia in shape, they are not related.  True petunias are members of the Solanaceae, the family that includes tomatoes, eggplants, potatoes, and nightshades.  Ruellias, the "wild petunias", are members of the Acanthaceae; a family that includes a great many tropical and semi-tropical plants commonly grown in Florida for their flowers - e.g. Justicia and Thunbergia.  The one characteristic that members of this family share is that their ripened seed capsules explode and send the seeds off a good distance away from the parent plant.  Because of this, all Ruellias tend to move around a landscape over time.
Wild petunia is one of the most adaptable and easy to grow wildflowers available to home gardeners in Florida.  Though it is most often encountered in sandy & sunny uplands, it will tolerate a great deal of shade and moisture as well.  I have found it in shady hammocks in nearly saturated soils and in pure sand in exposed scrub.  In the garden, it will grow nearly everywhere, though it will be leggier and bloom less often in shade.
Wild petunia is a long-lived perennial that dies back to the ground each winter.  Its leaves emerge in early spring and it quickly reaches its mature height of about 12-18 inches by late April - early May.  The leaves are ovate and opposite on the stem.  Often, many stems arise from the basal portion near the root mass and the plants develop a nice rounded form. 
Blooming occurs almost non-stop from late spring to late summer/early fall.  The trumpet-shaped flowers are about 1 inch across and vary in color from nearly white to a deep purple.  Often, they occur in pairs and they remain open for only one day.  I have found that butterflies relish the nectar from these flowers; in some of my gardens, they have been the top choice among nectar plants. 
Wild petunia scatters its seed everywhere in the landscape.  Once established, you will find new plants many feet from their parents, and after several years, you may find them in the front and the back yard - as well as everywhere in between.  Often, this is a good thing.  How many attractive wildflowers in your garden are this easy to propagate?  And, their small size does not make them crowd out larger neighbors.  But, it can be a nuisance to weed them if you are wanting a more formal look.
Wild petunia is one of the most widely propagated wildflowers in Florida and is grown by a great many nurseries affiliated with FANN - the Florida Association of Native Nurseries.  Be careful NOT to purchase the incredibly invasive Mexican wild petunia (R. simplex; syn. R. brittoniana; R. tweediana) pictured below, however.  They are very different plants and Mexican wild petunia...

has become extemely problematic to Florida's natural areas.  Mexican wild petunia spreads quickly from underground runners and is nearly impossible to eliminate without the use of herbicides.
Use our native wild petunia in mixed wildflower gardens.  Do not use it in large patches because it is absent in the winter and this will create bare patches of dirt that are unattractive.  Use smaller patches mixed with short grasses such as pinewoods dropseed (Sporobolus junceus) and wiregrass (Aristida spp.) and mix it with short wildflowers that maintain their basal leaves, such as pink penstemon (Penstemon australis).


  1. Thanks for the valuable information! We actually have some of the natives in our front beds.

  2. I love ruellia. Here in Southeast Texas I see a lot of R. nudiflora and to a lesser extent R. humilis. Really nice when you see a large patch of purple flowers decorating the side of the road.

  3. Craig, I am with you on the carolinensis being a problem sprouting up in all my beds and containers and anywhere it can blast the seeds to. I think this is also the place to point out the difference between the sterile tetraploid Ruellia Purple Showers and the invasive seedy type. You will know by the pervasive seeds and seedling if you have the wrong one.
    The plant you have in this picture above is the sterile Purple Showers which is much showier than the invasive species. The video on the IFAS site also misleadingly uses some video showing the distinct Purple Showers flowers and plants and characterizes them as the invasive without making any distinction between the vast expanses of the invasive type shown in most of the video. Florida growers have been exclusively producing Sterile Purple Showers since it became popular in the late 90's and not selling the invasive. We do not have invasive seedlings in our nurseries. We just have not been doing a good job at telling everyone what we have been doing. If articles like these pointed out the clear differences then startup and hobbiest nurseries would know which ones not to grow. I am a huge fan of natives and native landscapes and promoting the benefits. All native landscape are just not what everybody wants. We need to give gardeners all the facts so they can choose for themselves.

  4. Thanks for all the comments. One point I'd like to emphasize is that the non-native wild petunias sucker - even the sterile ones that don't seed. In landscapes I have worked on, I have found all the non-native varieties to be difficult to eradicate once established because the underground portions are never killed completely with either hand-pulling or by use of Round-Up. It takes several times - and this is a problem if they sucker into natural areas. Gardens are a different animal IF you can contain them to a garden plot...

    1. Agree wholeheartedly re the sterile Mexican petunia... We inherited a side yard full of it, and we’re beginning to get a handle on it, but it’s not easy!

  5. I cannot tell from this blog site who, if anyone, has seeds of Ruellia caroliniensis. If you do, please post your name and contact information. Thanks.

  6. I would just like to say no matter what you do DO NOT get the non-native version of this flower, it is literally impossible to get rid of. It grows profesuly in a short period of time and takes over all other plants. It is invasive and I was trying to get it out of my backyard for the past couple of days. Even though I did get what seems like all of it out, eradicating all of the countless roots underground seems impossible, and I've heard from many people it just grows back from the leftover roots. I can defintely see why this plant is invasive and it's not even that pretty so I warn anyone who reads this to just stick to something else.

  7. An update. Billy McCord, of the S.C. Dept. of Natural Resources, has given me native Ruellia caroliniensis plant from his garden. Here, it is a larval food plant for the Common Buckeye and White Peacock (per Daniels; Cech and Tudor). I was never able to find the seed.

    -- Jock Stender, Charleston, SC

  8. Glad you found a source for this wonderful widlflower - and let me know about its value in your area as a larval food plant. It is listed here, in FL, as a larval plant for both of those butterflies too, but I have never seen it used as such in my yard or those of my friends. Here, buckeyes mostly use false foxglove (Agalinus spp.) and white peacocks are most drawn to Bacopa monnieri. Most butterflies exhibit regional differences in their use of potential larval plants, so it is always important to know what the ones in your region tend to use before consulting a book that gives all possible choices. Wild petunia is always a good nectar source. If it proves to be a larval plant for you too, that is extra special. Thanks for posting.

  9. Yesterday evening I watched as our resident wild rabbit ate a sprig from the wild petunia I quite happily allow to grow in my garden. Who knew it was bunny food too?

  10. and I was shocked to see the nonnative Mexican petunia at Kanapaha Gardens this last weekend around the water garden... extremely thick!!! Could someone with a little "authority" on the subject please talk to them?!


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