Devil’s Claw

          Loose Devil’s Claws lie scattered across the ground here. Their stiff, recurved tentacles reach up through the low growth like up-turned hands. The animals prospecting through the dry weeds have to be careful where they step. On occasion, one of them gets caught. A hobbled jack rabbit or a coyote will then walk past in the embrace of the black bracelet – the thin, hooked arms closed around a foot or an ankle from both sides, holding firm.
           The larger claws will latch on to passing elk or pronghorn antelope. The animals will stop now and then – lift their foot and shake it, but the claw’s grasp holds tight. There are spurs at the base from which the two arms separate. Those spines only dig in when the claw moves up or down a leg – securing a grip.
          Eventually, those animals stand up on a rise, from which they can scan for trouble. If the lookout is clear, their attention shifts and they bend their head down and chew off the unwanted burden. They break one of the arms, and the black thing falls to the ground.
          But should something startle the animal, it bolts. The unwanted hitch-hiker does not slow them down much, but it may be carried for a mile before it is finally shed.

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              A plant produces the Devil’s Claws. They function as the plant’s seed dispersal agent. Being stationary, the plants must enlist the help of other organisms with their own reproduction. Seed dispersal is essential to their survival.
          Other groups of organisms are reproductively self-sufficient. The animals, and the microbes are mobile – able to move themselves together for mating. Their progeny are then able to move themselves apart and spread away to new ranges. These organisms manage their own reproduction.
          The plants, in contrast, cannot carry their own reproductive germ cells to each other. Their next generations cannot seek out greener pastures by themselves. They depend on the mobility of their animal pollinators for the union of their sexual cells. Many of them depend on animals for the dispersal of their seeds.
          The earliest plants dispersed their germ cells in the water, or on the wind. Much later on the evolutionary timeline, plants developed relationships with the animals. They produced flowers to attract attention. The animals afforded them much greater reproductive success.
          Once they began their association with the insects, the flowering plants came to dominate the flora of the world. They displaced many of the wind-pollinated gymnosperm plants, and the water-borne ferns and mosses.
          After the Cretaceous, the birds joined the insects in pollinating the flowering plants. The flowers diversified, and some developed fruit to contain their seeds. The birds then carried the seeds of those fruiting plants far and wide. Other plants came to grow a nutritious cap (eliaosome) on their seeds. Those are prized by ants, who carry the seeds to their hives. Seeds that find themselves transplanted between locations by the animals are in position to germinate into plants that will diversify into new habitats. Adaptation to new environments leads to the development of new plant species.

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          In recent times the plants have widened their relationships to include another group of animals – the mammals – on their list of seed dispersers. Devil’s Claws are an example. They are native to the arid reaches of the American southwest. Their seed pods split as they mature. The split ends twist as they dry – tapering into recurved arms that will grasp any leg that steps between them. The seeds then walk away from the plot where they were produced.
            Devil’s Claw seeds are relatively large, but then, they are carried by large seed-dispersers. They are borne stacked in single-file columns within the black pod. When the pod is attached to a moving animal, it may swing through a vertical orientation in time with the animal’s gait. A single seed is released with each step; the seeds in the column behind it then settle down a notch, each in its turn.
          Devil’s Claws have spread across the dry American southwest, from the Rio Grande valley to the Pacific coast. Their association with their mobile hosts is a “phoresis” – a relationship that provides the plants with seed translocation only, and provides nothing at all to the animal transporters.

Mature Devil’s Claw Proboscidea parviflora on the vine.

          In the very recent past – only twelve thousand years ago or less – the Devil’s Claws have broadened their relationship with mammalian seed dispersers. They were noticed by the early human migrants to North America, who moved into their range from the north. These people found that the young, green Devil’s Claw seed pods were edible. They found that black fibers, which could be stripped from the mature claws, could be woven into baskets, strengthening the weave.
          These people came to cultivate this plant. In the process, they may have selected for more palatable green pods, and longer hooks on the mature pods (1). The cultivated plants can be distinguished by their white seeds, altered from the wild-type black.
          More recently still, an extinction among the animals, including among the American Indians, has led to a decline of the Devil’s Claw plants. In their current context, their claws seem a curiosity – of no imaginable use. This is because of a nearly complete disappearance of the elk and antelope, and a precipitous decline in the other mammals in their range. Now the claws accumulate on the ground unmoved from where their vines grew earlier in the season. Their seeds do not disperse. The plant is in decline across its range.

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          The plants and the animals have adapted to each other over the eons. The plants have come to depend on their seed dispersers, and on their pollinators. Those pollinators import microbes that preserve the nectar in their flowers (2) which then attract further pollinators over the growing season. The plants send out chemical signals to attract animal predators, which suppress the herbivore populations. Well supported plants provide the food and the oxygen that supports the animals. Both groups have joined into a complex, ever-changing, mutual support network that sustains them all.

(1) Bretting, P. K. 1982 Morphological differentiation of Proboscidea parviflora under domestication. American Journal of Botany 69, 1531-1537

(2) Daubert, S. 2020 Chapter 12 “The Sweetest Niche” in Between the Rocks and the Stars.

P. parviflora inflorescence.