When the Wayne's Word staff began compiling a list of hitchhikers that are difficult to remove from socks and underwear, we felt confident that our list included the most tenacious species. That is, until horticulturist John Trager of the marvelous Huntington Botanical Garden in San Marino, California told us about a fascinating tree from Madagascar (Uncarina grandidieri). This amazing species definitely goes to the top of our hitchhiker list with 12 SRDUs (Sock Removal Difficulty Units). The hitchhiker seed capsule superficially resembles a grappling hook or a space satellite from a sci-fi movie. It has long radiating spines, each tipped with sharp hooks. In fact, Mr. Wolffia impaled his left fingers on the spines, and while trying to free himself, he also impaled his right fingers. His hopeless predicament was reminiscent of a Chinese puzzle where fingers of both hands are caught. How animals in Madagascar rain forests (such as Lemurs) free themselves of these incredible hitchhikers is a mystery.

Uncarina belongs to the pedalium family (Pedaliaceae), an interesting and little-known family that includes sesame (Sesamum indicum), source of the delicious seeds on your favorite hamburger buns. The flowers of Uncarina are remarkably similar to those of Devil's Claws (Proboscidea) and are undoubtedly closely related to the martynia family (Martyniaceae). John Trager of Huntington Botanical Garden was able to hand pollinate the flowers to produce the bizarre hitchhiker fruits. Unlike most flowers, the anthers of Uncarina do not split open to release powdery pollen. Instead, the pollen is paste-like and must be squeezed out of the anthers, sort of like squeezing toothpaste out of a tube; or like squeezing a blackhead to release the mass of fatty material in a skin pore. According to C. Hanson (Cactus and Succulent Journal Vol. 69, 1997), this act may be accomplished in nature by pollen-eating beetles. As the beetle chews on the anthers, the pasty pollen oozes out and gets on the beetle's thorax and elytra (outer wing coverings). When the beetle enters another flower and pushes past the lower stigma lobe, the upper stigma lobe is forced down and wipes pollen from the beetle's body.

One of the "super hitchhikers" of southern California, Baja California Norte, and the offshore California islands is a low-growing annual called "stick-tight" (Harpagonella palmeri). In the official Wayne"s Word Top 17 Hitchhikers, this species receives 10 SRDUs, although it is almost as difficult to remove from your socks as the previous species. This hitchhiking plant is occasionally encountered on dry slopes and mesas of coastal San Diego County. The fruit of this rare wildflower is composed of two small nutlets enclosed in a burlike calyx. The persistent calyx is armed with 5-9 spines, each with minute, hooked barbs. The generic name Harpagonella is derived from the Latin word "harpago" or grappling hook. Like a grappling hook, the burs become deeply embedded in fibrous material and are practically impossible to pull out.

Stick-tight belongs to the borage family (Boraginaceae), a large family of attractive wildflowers and several very effective hitchhikers. Hikers in the Sierra Nevada of California have undoubtedly noticed the little seed-bearing nutlets of a blue wildflower called forget-me-not or stickseed (Hackelia species) firmly attached to their shoelaces or socks. But when it comes to a hitchhiking bur that could render a pair of socks or fine-mesh cloth net worthless, Harpagonella gets the highest award. And a cold night in a sleeping bag, with "scratchy" stick-tight burs embedded in your long underwear, is an unforgettable experience.

Two more hitchhikers with Wayne's Word ratings of 10 SRDUs are krameria (Krameria grayi) and stick-tight (Desmodium cuspidatum). Krameria is a small, purple-flowered shrub of the Colorado Desert region of southeastern California. The amazing hitchhiker fruits are like miniature versions of the legendary Uncarina of Madagascar. The fruit is covered with radiating spines, each spine tipped with several minute hooks or barbs resembling a tiny harpoon. In a related species (K. parvifolia) the barbs are scattered along the upper portion of each spine. Although the flowers resemble a lovely orchid, krameria actually belongs to its own family, the Krameriaceae. Kramerias are also quite fascinating because they are partially parasitic on the roots of nearby shrubs.

Stick-tights or beggar's-ticks (Desmodium cuspidatum) produces slender legume fruits that break into small, one-seeded joints covered with tiny barbed hairs. Technically, this special kind of legume fruit is called a loment. The individual joints are so flat that they are exceedingly difficult to remove from your socks. Like little flat ticks, you must individually pull off each one. This can be exasperating when your socks are covered with them. Several species of this remarkable hitchhiking herb are native to the midwestern and eastern United States.

Naturalized hitchhiking plants often grow very well in disturbed sites, and this is how some of California's most noxious weeds were introduced. The earliest reported collection of puncture vine in California was made at Port Los Angeles in 1903, presumably the result of a ballast dump. Within a few decades it had spread throughout the state, reaching epidemic proportions in some cultivated valleys. The burs were carried in the wool of sheep, in hay, straw, other feed, manure, melons, alfalfa, cotton, potatoes, picking sacks and boxes, tents, sand, gravel, farm and industrial machinery, and in rubber tires of automobiles and airplanes. Puncture vine is the scourge of every bicyclist and is a major factor in the popularity of inner tube repair kits. Although it only has a SRDF of 3 in the above table, this may be a gross underrating for this naturalized hitchhiker.

Puncture vine belongs to the caltrop family (Zygophyllaceae), so named because of the shape of the wicked fruits. At matury, the fruit dries and breaks apart into five seed-bearing sections called carpels. Each section is armed with several sharp spines that readily penetrate bicycle tires or your shoes.

During medieval times, a vicious weapon called a caltrop was used in European warfare. This was an iron device with four points so designed that one was always facing upward, whichever way it landed, to impale the hooves of enemy cavalry horses. A similar device was also used in World War II to destroy truck tires on enemy supply convoys. The widespread water caltrop (Trapa natans) also has a four-pronged fruit that resembles a caltrop.

Certainly one of the most painful hitchhiking plants in the southwestern United States is jumping cholla (Opuntia bigelovii). Although it only received 5 SRDUs for removal from interwoven socks, the spines are exceedingly difficult to pull out of rubber soles and elastic human skin. Like other kinds of cholla cactus, the cylindrical stem segments are densely covered with slender, barbed spines. In fact, this species is sometimes called "teddy-bear cholla" because of its dense covering of spines. What makes this cholla so unique is that the stem segments or joints break off with the slightest touch and become firmly attached to various body extremities. Unlike the unrelated but truly amazing Mexican jumping beans and California jumping galls, this cholla doesn't really jump. If you barely touch or brush against the spines and then suddenly jerk away, the fuzzy stem fragment will be instantaneously upon you. Trying to pull out the barbed spines is not only frustrating and excruciating, but usually results in the joint or fragment becoming attached to another part of your anatomy. On a field trip to the Anza-Borrego Desert of San Diego County, several students attempted to remove a segment from a lady's shoe, only to have it transferred to the shoes of each chivalrous male. It finally ended up on the hand of a screaming (bleeding) student who promptly flipped it full force into Mr. Wolffia's groin region. From that day forward the Wayne's Word staff always carries a pair of needle-nose pliers when walking through jumping cholla country.

Closeup microphotography with a scanning electron microscope (SEM) reveals why the spines of jumping cholla are so tenacious and difficult to pull out of skin. The spine is covered with sharp, overlapping scales or barbs that lie flat and allow the spine to penetrate skin readily like a very sharp needle. When you try to remove a spine, you are pulling against hundreds of tiny scales. In the process, other spines penetrate the skin from all directions, making the extraction very painful and seemingly hopeless.

The easily fragmented stem segments of jumping cholla are one of nature's most effective methods of hitchhiking and vegetative reproduction. Thickets of jumping cholla covering entire hillsides or alluvial fans may have developed from fragmented stem segments that became rooted in the desert soil. Although jumping cholla produces flowers, the seeds of most populations are typically sterile and reproduction is accomplished without sexual reproduction (technically referred to as apomixis). You could say that jumping cholla is a master in the art of hitchhiking and cloning itself.

One of the most interesting cases of hitchhiking involves seabirds and a tropical pisonia trees of the four o'clock family (Nyctaginaceae), including Pisonia umbellifera and P. grandis. On some atolls of the South Pacific, pisonia is the only dominant tree on otherwise barren islets. Marine birds use the large, edible leaves to construct nests in the trees. Pisonia trees produce tiny white flowers in terminal, many-flowered clusters. Individual apetalous flowers have a tubular, petaloid calyx that resembles a sympetalous corolla. The lower portion of the calyx tightly enwraps the ovary and is persistent around the fruit as an anthocarp. The calyx base plus the enclosed seed-bearing fruit is the unit of dispersal. In some members of the Nyctaginaceae, the persistent calyx base bears sticky glandular projections that aid in dispersal by adhering to the bodies of animals. This is especially true in pisonia trees in which the numerous glutinous anthocarps stick to the feathers of seabirds. This is an effective method of dispersal to distant atolls and islands of the South Pacific region. Sometimes a hapless seabird is completely covered by clusters of the sticky anthocarps, to the point where flight is difficult or impossible. Unable to remove the water-resistant, glue-like anthocarps from its feathers, the seabird drowns in the surf and is consumed by ravenous beach crabs.

The seeds of some parasitic mistletoes are also coated with a very sticky substance that aids in dispersal by birds. Desert mistletoe (Phoradendron californicum), a common parasite on cat-claw acacia (Acacia greggii), produces juicy, bright red berries that provide numerous birds with food and water during the winter months. If you walk along a desert wash in the Colorado Desert region of the southwestern United States, you can often spot a black bird called the phainopepla (Phainopepla nitens) near clumps of mistletoe. This bird is easy to identify because of the conspicuous crest on its head. Mistletoe seeds are covered with a glue-like substance that sticks to the bills of birds. When birds try to clean their bills, the seeds adhere to the limbs of other trees and shrubs. The seeds also pass through the bird's digestive tract and are transported from one bush to another in the bird's droppings. In fact, this probably explains the derivation of the word mistletoe: from two Germanic words: mista (dung) and tan (twig); referring to bird droppings on a branch or stem. Apparently when the word mistletoe was first used in Europe, people were already aware of the dispersal of mistletoe seeds by birds.

There are literally hundreds of additional plant species with remarkable hitchhiking seeds or fruits that use animals for their dispersal agent. Some of the Large Hitchhikers On Big Animals, such as the North and South American devil's claws (Proboscidea and Ibicella) may have ridden on the legs and fetlocks of large extinct mammals that once roamed vast plains more than 500 thousand years ago. A large African hitchhiker by the name of grappling hook or devil's claw (Harpagophyton (syn. Harpagophytum) procumbens ssp. transvaalensis) rides on many present-day hoofed mammals of the vast South African veld. A member of the Pedaliaceae (like the number one rated Uncarina grandidieri), the octopus-like fruits have long, hooked tentacles that are a menace to the feet and jaws of wild animals and grazing cattle. Although they are large and very effective hitchhikers on large animals, they only received 7 Wayne's Word SRDUs compared with 12 SRDUs for their Madagascar counterpart Uncarina grandidieri. They can be removed from socks rather easily, except your socks may be irreparably damaged with tears and small lesions. As an agent for plant dispersal, you have probably carried some small hitchhikers on your body while walking through a grassy field or meadow. So the next time you find a little seed or bur clinging tenaciously to your socks, think about how far its ancestors must have hitchhiked and the many perils of its long journey.

Go To Article About Cockleburs and Velcro Devil's Claws: Hitchhikers On Big Animals Return To WAYNE'S WORD Home Page Return To NOTEWORTHY PLANTS Page Go To Biology GEE WHIZ TRIVIA Page Go To The LEMNACEAE ON-LINE Page