', {"anonymize_ip":true});

The Origin, Discovery, and Demise (Hopefully) of a Population of a Non-native Invasive Plant

Abstract: A newly-discovered population of the non-native Ruellia dipteracanthus probably had its origin as hidden rootstock in a gallon-container of a different wetland plant purchased at a local nursery. In the three years since its apparent planting, the species has become well-established in the immediate area. Efforts to remove the species have been initiated.

On 31 August 2021, I found a small population of the non-native Ruellia dipteracanthus (Nees) Hemsl. in the creek bed near my house on Salton Drive, Austin, TX.
https://www.inaturalist.org/observations/93431167
@centratex was the first to suggest this ID and it was subsequently confirmed by @eric_keith. This was the 2nd report of the species in the Austin area and the 3rd Texas location of this potentially invasive species (Keith et al. 2017). The species is native to Brazil and established in the wild in Mexico (Mowat 2017, Nees 1847, cited in Keith et al. 2017). I had not previously noticed the species even through I work regularly in this stretch of the creek bed removing other invasive species such as Ligustrum spp. and Chinese Tallow Trees (Triadica sebifera). Another non-native species, Mexican Ruellia (R. simplex) is common along the creek banks in this watershed, and it was only because I noticed a difference in flower color, leaf shape, and pubescence that I realized it was something different (and non-native). The clusters of R. dipteracanthus are in a mixed native herbaceous groundcover on a sand and gravel bar just a foot or so above the level of the adjacent perennial creek.

I wondered about the origin of this non-native species and expected that the source would be from some suburban yard in the watershed upstream of the location of the plants. On 4-5 September 2021, I criss-crossed the neighborhood streets flanking this reach of the creek, studying flower beds in the front yards of homes in the area. I covered an area of about 65 acres (26 hectares) including most of the immediate watershed of the creek as far as 0.5 mi (0.85 km) upstream of the population of plants. This is only a small portion of the 500-acre watershed upstream of the plants, but I found no other plantings of the species.

Returning to the plants with the intent of collecting a few voucher specimens, I noticed that the clusters of the species were in the same area as some Smooth Horsetail (Equisetum laevigatum) that I had planted on the creek bank about 3 years prior.
https://www.inaturalist.org/observations/93802354
Then it dawned on me: The new Ruellia plants were almost perfectly coincident with those clusters of horsetails, with just a few small clusters immediately downstream where they had probably recently spread. My theory now is that even though I had only purchased one 1-gallon container of horsetails to plant, the pot may have contained some unnoticed rootstock of R. dipteracanthus, and thus I inadvertently planted both species at the site. Moreover, I had split up the horsetails into about 3 or 4 small clusters to plant in an area of about 10 m x 20 m, and each of those horsetail clusters now has a vigorous associated colony of the Ruellia.

That realization changed my goal: I immediately made plans to begin the process of removing the non-native Ruellia from the location. In that effort, I soon found that the species grows in dense clusters with vigorous rhizomes, a deep root system, and that stems bent over by floodwater were also commonly rooting at the nodes. Aboveground stems easily broke off at ground level nodes, a strategy which would benefit the plants and make them efficient colonizers under disturbance regimes like flood events.
https://www.inaturalist.org/observations/93802355
The effort to remove the easily reachable clusters of plants will take several days of digging in the sand, gravel, and cobble of the creek bed. It is likely that regrowth of some plants will occur in future growing seasons and that retreatment and vigilance will be necessary to ensure that all material has been removed. This is not a new type of effort for me. I previous undertook the removal of invasive Elephant Ears or Taro (Colocasia esculenta—not originating from me!) along this same stretch of creek and that effort took a few years to complete and requires continuing monitoring.
https://www.inaturalist.org/observations/1914012
https://www.inaturalist.org/observations/19376164
https://www.inaturalist.org/observations/19686222
https://www.inaturalist.org/observations/2116918

References:

Keith, E., J. Wright, and W. Godwin. 2017. Naturalized occurrence of Ruellia dipteracanthus (Acanthaceae) in the USA. Phytoneuron 2017-57:1-3.

Posted by gcwarbler gcwarbler, September 06, 2021 02:26

Observations

Photos / Sounds

Observer

gcwarbler

Date

August 31, 2021 02:46 PM CDT

Description

So I need some Ruellia help here. I have two very distinct species of Ruellia growing along the creek bank and gravel bars behind Salton Drive. This one is the mystery species. It has very fuzzy long-petioled, narrow lanceolate leaves, pubescent stems, and large, purple, single axillary flowers. It is apparently rhizomatous since it forms fairly dense low colonies. It grows up to 30 to 50 cm high but is heavily browsed down by deer. It doesn't match any of the regular native species with which I'm familiar (nudiflora, humilis, drummondiana, metziae, occidentalis). Compare with R. simplex, growing within a few yards along the same stretch of creek:
https://www.inaturalist.org/observations/93431166
@franpfer @joshua_tx

Photos / Sounds

Observer

gcwarbler

Date

September 5, 2021 09:30 AM CDT

Description

These images offer further documentation of the small introduced population of Ruellia dipteracanthus that I found several days ago. See,
https://www.inaturalist.org/observations/93431167
The present observation documents several clusters of the species. There are about 5 or 6 clusters of the plants scattered over a sand and gravel bar in an area about 10 m x 20 m. The first image here is literally the same cluster of plants shown more closely in that earlier observation. Notice the presence of Horsetails in/around each cluster of the Ruellia.

Photos / Sounds

Observer

gcwarbler

Date

September 5, 2021 09:48 AM CDT

Description

These images offer further documentation of the small introduced population of Ruellia dipteracanthus that I found several days ago. See,
https://www.inaturalist.org/observations/93431167
I began the process of digging out the Ruellia dipteracanthus to prevent/limit its further spread in the creek bed. I quickly found that the species is aggressively rhizomatous and also spreads by rooting at the nodes of decumbent stems. This set of images documents the stems, rhizomes, and root systems of several plants that I had just dug up. See the accompanying observation of the clusters of plant before this work was started:
https://www.inaturalist.org/observations/93802354

Comments

Chuck, I enjoyed the back story. It read a bit like a classic "who dunnit". : ) This species is a new one for me. I'll have to keep my eyes out for it going forward.

Posted by centratex 3 months ago (Flag)

Yep, "I dunnit!"

Posted by gcwarbler 3 months ago (Flag)

Add a Comment

Sign In or Sign Up to add comments

Gracias al apoyo de:

¿Quiere apoyarnos? Pregúntenos cómo escribiendo a snib.guatemala@gmail.com