Fictional Botany: Spiculogramina greenii

Note from Mr. Subjunctive: This post contains two references to people, included because it amused me to do so. One is a real, if obscure, person and a work of his/rs, which is moderately straightforward if you happen to know it to begin with. The other is roundabout in a way that will give away the joke if I describe it, but the person in question is probably more widely known. I will award 50,000 PATSP points to the first person who can identify either reference.¹

Spiculogramina greenii, which goes by the common names cut the devil down, kingwah, sharpgrass, Confederate razor blade, and African rat grass is a plant in the family Poaceae, common in dry, warm climates throughout the world. Though superficially similar to Cladium jamaicense, or sawgrass, Spiculogramina is a true grass, not a sedge, with round stems (Cladium stems are triangular in cross-section) and broad, alternate leaves (Cladium leaves are narrower and arranged in spirals).

It is of substantial economic significance, because it is a very aggressive competitor for resources and because it provides a protective habitat for a large number of harmful insects and rodents. The International Council on Invasive Plant Species, or ICIPS, lists Spiculogramina greenii as number two on its Most Destructive Plant Species List, after Pugnaxis robusta (common names: fighting banana, Dawson's banana).

Spiculogramina is native to Northwestern Africa, where it grows in marginal areas with little rainfall, though it is not, strictly speaking, a desert plant, and does not grow in the Sahara. The plant is a perennial. Long (to 7 ft / 2.1 m), narrow (to 4 in / 10 cm wide), semi-rigid leaves sprout from thick rhizomes, particularly following rains. Leaf edges contain spiny, silica-containing projections which are capable of cutting flesh and harbor bacteria which can cause serious infections. The genus name refers to these silicaceous spines (spiculo- for sharpened, pointed + graminus for grass).²

Given favorable conditions, one seed may become a dense sod of rhizomes covering 300 square feet (28 sq. m) during a single year. This is facilitated by the plant's secretion of allelopathic compounds into the soil, which kill or stunt competing plants. All parts of the plant are also poisonous to most animals, though in its native habitat, leaves are eaten by several species of beetle and the caterpillars of four or five moths, and the stems are hollowed out and eaten by a particular weevil.

Spiculogramina also produces two distinct types of roots: deep taproot-like ones, which frequently reach eight to ten feet (2.4 to 3.0 m) into the soil, and thinner roots with small (to 0.5 in / 1.2 cm in diameter) watery nodules along their length, which store water. Both types of root, as well as pieces of the rhizome, are capable of sprouting new plants if severed. The plant also uses C4 carbon metabolism, another adaptation to the infrequent or erratic rains and heat in its native environment.

The wind-pollinated flowers may appear at any time of year: plants are therefore a continuous source of seeds. Plants are mature enough to flower after two months of growth. Seeds are small, lightweight and downy, and are consequently capable of traveling large distances by wind. Spiculogramina seeds are irregular germinators: in any given batch, only about 20% of new seed will germinate immediately upon landing; 8% will germinate in the following year, 5% two years later, and so on. Seeds known to be fifteen years old may still be viable under certain conditions, making total eradication extremely difficult.

The dense stands formed by Spiculogramina frequently shelter nocturnal rodents, specifically rats and mice, which have protection from predators in the form of the sharp, rigid leaves, water, which collects in small shallow pools among the closely-packed rhizomes, and a tiny amount of food in the form of seeds and insects. Generally, rodents leave the stands to forage elsewhere at night, then return and spend the day among the Spiculogramina. The abundant rodents and pools of water attract more visitors, in the form of mosquitoes, who can treat the Spiculogramina stands as one-stop shopping for blood with which to form eggs, and water in which to lay them.

As one can imagine from this description, this is an extremely undesirable plant, even in its home range. The native word for the plant, kingkua'dgene'bu, translates approximately to the common English name cut the devil down (kingkua'dgene'bu is also the source for another common name, kingwah). Eradication, however, owing to the plant's remarkable capacity for regeneration from root and rhizome fragments, prolific seed production, and staggered germination, is all but impossible to achieve without the persistent and dedicated application of herbicides. The most frequently used are glyphosate (Roundup), clethodim (Select) and sethoxydim (Poast), though glyphosate-resistant stands have been reported. So far, all such stands are located in the Caribbean.

The World Health Organization is experimenting with techniques for freezing the plants in place using rapidly decompressed air (Spiculogramina cannot survive even brief exposure to temperatures below 10F/-12C, though this includes the rhizomes and surface roots as well. It is less clear whether the taproots are as cold-tolerant as the rest of the plant.); dry ice and liquid nitrogen have also been used. To date, the WHO is cautiously optimistic, though some have questioned the practicality of this method, which is quite expensive, needs to be repeated frequently, and is of uncertain benefit. (Dry-ice treatments are particularly opposed, as errors during application can have the dual consequence of failing to freeze the plant enough to kill it and infusing the air around the plant with extra carbon dioxide, enabling it to grow even faster than it otherwise would have.) Some private companies in the southeast U.S. offer liquid-nitrogen treatment for stands of Spiculogramina, though treatment needs to be repeated approximately every six months to keep the plant manageable, due to the seeds which are almost certainly present in soil.

Covering stands of plants with black plastic is also somewhat useful, though plastic is difficult to apply on fully mature plants and tends to tear on leaf edges. Spiculogramina can also survive short periods of extremely warm temperatures (to 140F/60C), so application can only be done on days which are already very hot and expected to remain so for several days. A U.S. company is developing a black polypropylene sheeting product for control of Spiculogramina which is sturdy enough to resist puncture, can be reused up to five or six times, and is fully recyclable. It remains to be seen whether such a product can be marketed at low enough cost to make it practical for widespread use. Black-plastic treatment of Spiculogramina also leaves large amounts of debris behind, which can still shelter animals, remains sharp enough to cause injury, and is highly flammable. Until disposal of the waste material can be streamlined, this will probably not be a primary method of eradication.

Burning of Spiculogramina is also not considered practical, as there is some evidence that fire increases the germination rate of seeds, and Spiculogramina fires burn very hot and are very difficult to control.

Biological control is generally thought not to be an option for control of Spiculogramina, as the beetle, caterpillar and weevil species which feed on it in its native habitat are all either known to feed on desirable plants or are unable to complete their life cycle outside of their native range (due to climatic conditions and/or symbiotic partnerships with other plant and animal species).

Spiculogramina has spread to many tropical and semi-tropical climates around the world during the Twentieth Century; this is thought to be primarily due to seeds being inadvertently transported in airplane cargo holds. The southeast U.S. has a much longer history with this plant than most other areas where it has become invasive: Spiculogramina appears to have arrived in North America and the Caribbean at roughly the same time slaves were being brought there from Africa, primarily in the seventeenth century. Legends suggest that at least some of the introductions of Spiculogramina were deliberate acts of sabotage by Africans against their captors, though there is also one well-documented case of South Carolina plantation owner Richard Derbyshire deliberately cultivating the plant in 1845, hoping to use the strong leaf fibers in the manufacture of cloth, rope, and paper. (He was unable to do so competitively, and was already nearly bankrupt before the Civil War happened and put him completely out of business.) Today, Spiculogramina is found throughout most of the eastern half of the United States, kept at bay only in parts of New England and the Upper Mississippi Valley by their winters. It is hardy to USDA Zone 5B. The worst infestations still tend to be in the Deep South, particularly abandoned or uncultivated land in MS, AL, GA, SC, and FL, throughout the Caribbean, and in coastal Australia.

On a happier note, Spiculogramina may prove useful in controlling other weeds: the allelopathic chemicals it produces are being investigated for use as herbicides, in particular against Ailanthus altissima, the "tree of heaven." There is also renewed interest in Spiculogramina as a source of paper and rope, as stands regrow almost as soon as they are cut down, and Spiculogramina-fiber products are generally sturdy and of high quality. Some have suggested that its deliberate cultivation could be useful in fixing atmospheric carbon dioxide, since the plant can grow very quickly and takes up a considerable weight of CO₂ in the process.³ It is unclear how this could be done without spreading the plant to ecologically-sensitive habitats, however. Scientists are also interested in the toxins the plant produces, which are thought to have promise as medications in the treatment of some forms of cancer and certain metabolic disorders.

The genus Spiculogramina also contains two other African species and one Madagascan one:

S. marsterei is a smaller (to 4 feet / 1.2 m) plant with a similar form as S. greenii. Unlike S. greenii, new growth emerges very pale yellow and gradually darkens with age. S. marsterei's leaf margins also contain silica-based serrations, though they are much smoother and less likely to cause injury than those of S. greenii. Though found in the same native region, it does not appear to be particularly widespread and is not considered likely to become invasive, because its seeds are heavier (reducing spread by wind), fewer in number, edible, and produced only between April 1 and May 15, instead of year-round.

S. pachyphytum is found only in the extremely dry regions of Western Africa abutting the Sahara Desert. Its leaves have adapted to the climate by becoming shorter and thicker, taking on a rodlike form tipped with a sharp terminal spine. They are also usually covered with fine grayish hairs, which deflect the intense sunlight, retain moisture, and provide some camouflage against predation. Leaves are usually very close to vertical during the day, but spread slightly more open at night. The plant is only 1 foot (0.3 m) tall at maturity, and is extremely slow-growing. Flowers appear quickly following rain and are self-fertile. Seeds are spread by wind, as for S. greenii, but are viable only for a short period of time, unlike S. greenii.

S. madagascensis is approximately the same size as S. greenii but has broader, dark green leaves with narrow, bright yellow, non-silicaceous margins. It grows much more slowly than other members of the genus and does not appear to pose a significant invasive threat, though it is on most watch lists, because its seeds are spread by wind and germinate irregularly, and it is, like S. greenii, highly flammable. Its natural range appears to be limited to the island of Madagascar.

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² The specific name, greenii, refers to the American botanist Keith Green, who first described it in Africa in 1981.
³ Spiculogramina greenii has, in fact, been measured as the second or third most efficient converter of carbon dioxide to biomass in the plant kingdom.