Story by Anita Westervelt
It began with a silly remark while answering questions after a South Texas Border Texas Master Naturalist chapter meeting presentation where I was asked would pink mint grow in a certain place. I’d already mentioned how very prolific the winter-blooming butterfly-attracting plant was in full sun, and the enormous number of seeds it produces; my answer was: pink mint (Stachys drummondii) could probably grow in the cracks of your sidewalk.
After quite a bit of research, I have no proof that it does and no proof that it doesn’t, but that quip had piqued the interest of one of our Texas Master Naturalist chapter sponsors, Tony Reisinger, Cameron County Extension Agent for Coastal & Marine Resources with Texas Sea Grant at Texas A&M University and the Texas AgriLife Extension Service, who asked, just what are all those plants that grow in the cracks of sidewalks?
After an exchange of photos, comparing Tony’s east end Cameron County sidewalk plants to my own stockpile of photos from the middle of the county, certain plants appeared to be more prone at taking advantage of the opportunity to be noticed by wedging themselves in between tiny cracks of pavement. Of course, once the roots get beyond the depth of the concrete slabs, a world of undisturbed soil is a veritable playground for plant roots regardless of whether we want them on the upside, or not.
What was to be a fun little missive about a handful of errant plants has turned into a much longer read. Be prepared to spend about 10 minutes here or read it in sections, but the shenanigans of some of these common sidewalk sightings might surprise you!
One of the more tenacious plants taking advantage of this between-the-cracks environment is three-lobed false mallow (Malvastrum coromandelianum). This plant is well-secured to the ground no matter where it puts down roots and impossible to eradicate by tugging at it without digging it up with a shovel – an impossible feat in the middle of a sidewalk.
To begin with, the plant has a strong tap root that may well reach to China, or so it seems when attempting to uproot it by pulling on it by hand. The tap root is so strongly bound to the earth, it cannot be pulled without breaking it off – which presents a worse problem as the remaining root system reproduces at the nodes – out of sight.
Three-lobed false mallow also is commonly called yard mallow, presumably because it loves comingling, without compunction, with a beautiful lawn. At first glance, the interloper’s leaves are rather exciting; they are small, dark green, crisp-looking, sturdy, shapely and tooth-edged; dotted amongst the leaves are tiny yellow five-petaled flowers like miniature buttercups about a quarter of an inch in diameter. The flowers open in late afternoon.
Left on its own, three-lobed false mallow can grow to three feet tall; more often it peaks at 18 inches and topples, making it more of a sprawler. The plant is an introduced species, native to an island in the Caribbean. For those plants in open spaces, if you dig deep enough with a shovel, the plant can be removed with taproot intact.
This plant is not without merit; it’s one of the known food plants for common and tropical checkered-skipper butterfly caterpillars and it blooms in all seasons, providing nectar – it’s a tradeoff. The plant is prolific, taking over sections of lawn, creating a tightly compacted ground cover which can be kept low with mowing – or left for hungry rabbits and Texas tortoises.
The second worst hard-to-get-out-of-the-sidewalk-crack plant is Runyon’s violet wild petunia (Ruellia nudifora). A photo provided by our chapter president and archeologist, Donna Otto, captured the plant sneaking through a sidewalk crack next to her screened porch in Hidalgo County, near Estero Llano Grande State Park, south of Weslaco.
I have a lot of this native plant. Attempts to pull it out when wedged between cracks of pavement are futile. It is said to have amazing roots that are at least five times the length of the plant, which is generally at least eight inches tall. The roots also spread underground via rhizomes.
But it’s pretty. Its claim to Rio Grande Valley fame is that it is one of the few plants that will grow in the shade. A more amusing attribute is that its fruit is dehiscent, which means bursting open, shooting seeds out from a seedpod. More often than not, there will be a butterfly, big or small, deep in the open, tubular depths of its flower, drawing nectar. It is host to common buckeye and pale-crescent butterflies.
Another plant in this between-the-cracks gardening was depicted in a photo sent by Joseph Connors, our chapter Webmaster and mothing and spider expert. He had found it growing through a crack in his sidewalk toward the western part of Hidalgo County and included it in his observations at www.iNaturalsit.org where it was identified as scarlet spiderling (Boerhavia coccinea).
I was really thrilled when I opened his photograph and saw the leaf shape of this fun-looking plant. Only once near our property did I find a spiderling, identified as erect spiderling (Boerhavia erecta), to include in my spring City Nature Challenge observations. The leaf of the two mentioned spiderlings is a sort of ace-of-spades shape with obvious venation (botanically speaking the leaf blade is described as broadly ovate, blunt and slightly wavy; B. coccinea is densely hairy.) In erect species, the leaf stems and venation are beet red, in striking contrast to its green leaves; B. coccinea leaves, in Joseph’s photo, were green and somewhat edged with a reddish-brown hue.
The flower, as the common name alludes, is vibrant red. Spiderlings are in the Nyctaginaceae (Four o’clock) family and are considered pantropical – meaning their distribution is one which covers tropical regions of both hemispheres. Southern California claims it as native, but the plant is naturalized throughout the tropics, happy in any soil. After reading up on this plant, it’s a wonder the Valley, if not the world, isn’t covered in scarlet spiderlings.
A University of Florida site described it as having a short, but thick taproot and cautioned against hand-pulled attempts which commonly cause the taproot to break off and re-sprout. The site further mentioned that little is known about herbicide efficacy for control. Apparently, Florida peanut farms are adversely affected by this plant, as it interferes with nutrients needed for the desired crop. The seeds are sticky, easily transported by sticking to the fur of animals.
Here, as in California and even Central Australia, scarlet spiderling is host to white-lined sphinx moths and possibly other hawk moths.
Other likely plants in local sidewalk-cracks are those in the Euphorbia family. Most likely they will be prostrate sandmat (Euphorbia prostrata), matted sandmat (Euphorbia serpens) and eyebane (Chamaesyce nutans) [Euphorbia nutans]. Prostrate sandmat has long shaggy hairs and hairy seed capsules. Matted sandmat is hairless and widespread in North and South America and can be found on most continents as an introduced species. It seems to clear a void for itself on the soil that would reach beyond a yardstick if one were tossed upon it. In the ground, matted sandmat roots at the nodes.
These sandmats barely have a root system; the taproot in the center is easily removed. Do note, the plants are prolific seeders. They bloom in all seasons, but you may have to squat down with a magnifying glass to see the tiny white flowers. If the plant is used by anything other than ants, my research wasn’t giving it up.
Eyebane (E. nutans), on the other hand, is useful in the garden but not so much as a pavement-crack-plant where its growth is generally stunted. Eyebane is a wispy, benign plant that might reach to three feet tall before its noticeable. It has lovely, tiny pink-turning-to-white flowers on airy, spindly-but-erect stems that wouldn’t look out of place in a fantasy fairy garden. It’s another one of those plants that may be populating sidewalk cracks nearly worldwide. On the plus side, the flowers provide nectar to bees, wasps and Syrphid flies; mourning doves and prairie chickens eat the seeds.
An entirely annoying, spindly, sprawling, prolific, pesky, leggy but nearly insignificant sidewalk-crack pop-up and lawn and garden intruder is straggler daisy (Calyptocarpus vialis), a shade-loving plant with odd common names, like horseherb, prostrate lawn weed, carpet daisy and creeping Cinderella-weed. It’s native to the southern United States, Mexico, Belize, Venezuela and the Caribbean, but seemingly well-travelled as it has been introduced to Argentina, Hawaii, India, Java, Australia and Taiwan.
Straggler daisy is in the Asteraceae Family. Although it tries to camouflage itself by nearly matching the color of grass, it soon begins sprawling over larger and larger areas. Hardly noticeable are the yellow flowers that barely reach to a quarter of an inch. This plant blooms during all seasons in the Valley, not only blooming, of course, but producing fruit, seeds and new plants. As with many sprawling and prostrate plants, there is one tap root; this one’s is wimpy and the plant can easily be hand pulled.
A real horror story about plants wedged between sidewalk and driveway cracks is nutgrass or nutsedge, specifically purple nutsedge (Cyperus rotundus), a perennial. This is probably the worst possible upstart to bolt up through the cracks of pavement. “Pulling nutsedge will increase the number of plants because dormant tubers are activated,” according to a Kansas State University, Johnson County Kansas Internet research and extension paper. It’s not a grassy or broadleaf weed; common herbicides have little or no effect on its control.
If you’re not familiar, the ditty, “sedges have edges,” means all nutsedges have triangular stalks, no matter how short they are. In ground, this plant can reach upwards of two feet; in sidewalk cracks, up to eight inches tall. Decimating the plant to the pavement with a weed-eater makes it appear dead – but it’s not. When left to develop, several golden-brown flower spikelets appear at the top of the stem.
Tony’s photo hopefully is some kind of local grass. I say hopefully because further research on the purple nutsedge reveals that it’s highly invasive and immune to chemical warfare. Please don’t hate me, but yes, I’ve taken drastic measures upon occasion, but to no avail.
Purple nutsedge has been “considered one of the world’s worst weeds, having been reported in more than 90 countries where it grows as a weed infesting at least 52 different crops worldwide.” It’s been described as having insidious and rapid growth and herbicide tolerance. Source: CABI.org, an international, inter-governmental, not-for-profit organization’s Invasive Species Compendium.
Patio pavers provide their own breed of crevice plants, like the pretty leaves of tropical amaranth, or low amaranth (Amaranthus polygonoides). This plant is easy to recognize because it has an interesting whiteish-gray, water-mark-like pattern on each leaf, like a chevron on a sailor’s uniform. It’s found in the Caribbean and in North America in coastal areas of Florida, South Carolina, Texas, Mexico and also in the West Indies and northern South America. It is in the Amaranthaceae Family, rather rudely known as the Pigweed family, most likely because the plants were used as pig fodder at one time.
The plant produces small, greenish flowers in dense clusters at the leaf axil and in turn becomes a prolific seed-producer of the exploding dispersal type. Take heed: the smaller the plant, the easier to remove.
Locally, there are other Amaranthus species, like Palmer’s pigweed, which can grow six to 10 feet in height and produce a thick vegetative stalk that spits a wet substance when whacked with a machete, or crushes and drenches gloves when attempting to pull it out by hand. This opportunistic plant certainly is not going to be pulled up by the roots and is one not to be retired to the compost pile due to the amazing number of seeds it can produce.
One of my favorite unplanned plants that comes up between sidewalk cracks and patio pavers is common purslane (Portulaca oleracea). The stems of this prostrate plant are hairless and can be as long as 20 inches. It blooms spring through fall. The flowers are tiny and have five yellow petals and yellow anthers. The flowers produce numerous small seeds that can remain viable in the soil for a least 30 years. The flowers attract flower flies, small bees and beetles. The seeds are a minor source of food for sparrows and songbirds; white-tailed deer and pigs feed on the foliage.
An annual, it comes up from a taproot that holds strongly to the earth; the good news is that it does not root at the stem nodes. Historically, the petals were eaten by humans as a source of vitamin C, but as discerning folks, look for more modern means for vitamin supplements (like at the grocery store) and not from a sidewalk garden.
Posies in tiny cracks next to buildings provide unique but incongruent scenes. A few of my favorite photos include Drummond’s woodsorrel (Oxalis drummondi). The first spring I noticed the flowers blooming in our yard, they were startling pretty with a neon pink-violet sunrise glow, so I didn’t mow them down, thinking insects might use them.
By September, the few plants were still pushing out blooms and were still pretty, so I kept them – the next spring, it seemed a quarter of the acreage was abloom in oxalis. Amazingly, this species is endemic to Texas, so it is not considered invasive, but it’s certainly aggressive, prolific and high-volume. It arises from bulbs, but I wouldn’t be surprised if the five-seeded dehiscent fruit capsule (remember, exploding, spewing like shrapnel) adds to the speed of propagation.
It’s rumored that the leaves, which look like a weird clover, were good in salads, despite the fact they contain oxalic acid, which is toxic. It may be a host plant for the cyna blue butterfly whose northern most range is at the lower edge of the Rio Grande Valley. Other than for fun photo ops, I didn’t find a lot of use for this native plant, but as wood sorrels go, it’s ok. Its cousin, on the other hand, is one to be watched.
Creeping woodsorrel (Oxalis corniculata), has shamrock like leaves but without the Irish luck. One color form has green foliage, the other purplish foliage.
The plant can become a pest, however, the little yellow flowers are rich in nectar and pollen and attract honeybees, carpenter bees, small leaf-cutting and other bees, Syrphid flies, small butterflies and skippers. The wedgling moth uses it as a host plant. This species, too, contains oxalic acid. Cottontail rabbits and white-tailed deer can browse it, but it can be toxic to other farm animals if eaten in quantity. It’s suggested to control these plants by hand or hoe weeding and best to do it before they set seed. The species is widely naturalized with obscure origins.
Some pavement sprawlers aren’t all that aggravating. I’ve saved my favorite for last: Berlandier’s trumpets (Acleisanthes obtus).
I was drawn to these flowers one early overcast morning because they looked to be white flowers with pink polka dots. I love polka dots, but upon close inspection, the dots were the pink anthers of the pale pink stamens. I’ve mostly seen these plants coming up from where our retaining wall meets the paved ramp off the driveway and where the courtyard wall bricks meet the driveway, although my first sighting was a spill of blooms over the edge of a retaining wall. The plant is a vine; one year one twined with climbing milkweed and possum grape vines, rising from the base of a mesquit tree. The three vines travelled together far into the tree canopy.
The plant's leaves are pretty, too. They are unequally sized to about one inch; they are crisp and break when bent. Botanical experts would say the blades are triangular to ovate in shape.
A local name for Berlandier’s trumpets is vine four o’clock. They are in the Four O’clock family, and not surprisingly, they open at four o’clock in the afternoon and close by sunup, except on cloudy days. They bloom in all seasons. These plants were the least affected in our acreage after the dastardly 2021 extended winter freeze. I have at least half a dozen plants; I keep them because they are pretty and don’t harm anything, but also, they keep coming back even when snapped off by the weed eater.
They are impossible to eradicate without digging out the roots, which I suspect travel down to the water table, and really, why would anyone try to remove these plants? The vines that grow from between the cracks don’t try to take over entire driveways, generally only spreading out about two feet. The flowers are an excellent source of nectar for night-flying insects; they are pollinated by moths; the plants are host to the white-lined sphinx moths; and the tiny white trumpets glow in the light of the moon, greeting those of us who wander outdoors at dawn.
