Palmer’s Grapplinghook

Palmer’s grapplinghook (or stick tight, Harpagonella palmeri) is an unobtrusive little plant considered “fairly endangered in California” by the California Native Plant Society. It has a bizarre fruit, from which it gets its common and Latin names, and which has earned it the dubious recognition as an ultimate hitchhiker.

In 2021, Palmer’s grapplinghook made a sudden appearance in one revegetation area on Stonebridge Mesa, where it formed large patches. covering much of the bare ground among the newly planted species.  Palmer’s grapplinghook had not previously been recorded on our list of plants in San Elijo Ecological Reserve.

Where did it come from? Will it persist?

Description ^{2,59,261,400,530}

Palmer’s grapplinghook resembles several of the popcorn flowers (Cryptantha spp., Plagiobothrys spp. and Petrocarya spp.) ⁵²⁹ from which it is distinguished primarily by its fruits. Palmer’s grapplinghook is a low annual plant that produces many long stems from a central point that lacks a basal rosette of leaves. Stems grow over and through neighboring stems forming a low tangle. Leaves are small and rather sparse, less than 1.5 inches (3.5 cm) in length and linear or lanceolate or slightly crescent-shaped. Leaves and stems are covered with short, stiff bristles.

The small flowers are bisexual and radially symmetrical, usually less than 1/8 inch (3 mm) across. Like other popcorn flowers, flowers are sequentially produced along one side of an uncoiling stem. One or two buds open at the top of the spiral, and  fruits develop along the straightening stem.  There are five bristly sepals united into a short lobed tube. Five white petals form a short tube that flares into five rounded lobes. Yellow appendages form a ring around the flower throat. There are five anthers and one pistil with a style and capitate stigma; neither anthers nor style project beyond the throat. Primary bloom is March into May.⁷

As the fruit matures, it twists around on its stem. Two sepals enlarge and partially unite, forming a hood that arches over the developing nutlet. The hood has several stout projections (spines), which are covered with strong, bristles, the entire structure reminiscent of a homemade grappling hook.

Classification ^2,11,44,143

Palmer’s grapplinghook is a dicot angiosperm in the borage family (Boraginaceae). Plants in this family are usually covered by stiff hairs, have flowers that develop along one side of an uncoiling (“scorpioid”) stalk and fruit that split into 1-4 one-seeded nutlets. Many of the best known members of this family are non-native garden flowers, such as garden heliotrope and forget-me-not.⁴¹ Plants in the borage family that are found in the Reserve include fiesta flower (Pholistoma auritum), coast fiddleneck (Amsinkia menziesii) and common cryptantha (Cryptantha intermedia).⁴⁸ 

Within the large borage family, 18 genera, including Harpagonella, are usually classified in the subtribe Amsinckiinae,⁵³⁰ many of which are known by the common name “popcorn flower”.

Palmer’s grapplinghook is currently considered the sole species in the genus Harpagonella, although a second species has been recognized.⁵³⁰

Ecology

Seeds of higher plants are often dispersal units,⁴¹ moving the next generation of plants away from the parents, avoiding competition for light, water and nutrients, and expanding the population into new areas. Seeds have adapted to make use of many modes of transportation, such as air, water, ballistics, gravity and animals. The most irritating of these seeds (from a human perspective) are undoubtedly the bristly and hooked seeds that cling to parts of passing animals, including bird feet, animal fur and human clothes. In spite of the large numbers of seeds that get pulled out of socks and sweaters, these hitchhiking seeds are produced by less than 5% of plants.⁴¹ As its name implies, Palmer’s grapplinghook is one of them.

In an informal survey in the southwest U.S.,⁵²⁸ annoying hitch-hiking seeds were ranked in order of  Sock Removal Difficulty Units (SRDUs). Among the 14 top ranked species Palmer’s grapplinghook (the study calls it stick-tight) ranked number one with 10 SRDUs, out hitchhiking the infamous castor bean (Xanthium strumarium ) by two whole units. “A cold night in a sleeping bag with ‘scratchy’ stick-tight [Palmer’s grapplinghook] burs embedded in your long underwear, is an unforgettable experience.”

However, in a broader survey, Palmer’s grapplinghook was out hitchhiked by a tree from Madagascar, Uncarina grandidieri, which earned 12 SDRUs.

Human Uses

We can find no no reports of Palmer’s grapplinghook being used by people.

Interesting Facts

As this description was being prepared, a second species was found among the grapplinghooks. The two plants were almost identical in overall appearance, and were recognized by the dissimilar fruit structure – one a grappling hook, the other a spiny marble. This second species appears to be adobe popcorn flower (Plagiobothrys acanthocarpus). By mid-May, the grapplinghooks had dried and the still-green Plagiobothrys stood out clearly. Like Palmer’s grapplinghook, adobe popcorn flower had not been previously described from the Reserve.⁴⁸