Plant 284

Claytonia perfoliata Donn ex Willd. (Montiaceae)

Miner's lettuce

The genus Claytonia comprises 27 species of annual or perennial plants that are indigenous to North America and eastern Asia. The generic name was created by the Swedish botanist Carolus Linnaeus to commemorate the eighteenth-century English Colonial botanist John Clayton, one of the pioneering plant collectors in North America.

Claytonia perfoliata, a spring-flowering, fleshy, herbaceous annual, is native to western America, with a natural range extending from British Columbia south to Central America. As plants grow, they produce two types of leaves. Rosette leaves have long leaf stalks. Leaves on flowering stems are paired and their bases are connected, so that they appear to be a single circular leaf, which is the origin of the plant's species name.

In the mid-twentieth century, it became possible to investigate easily the number and structure of plant chromosomes. It was soon discovered plants can increase the number of entire sets of chromosomes in their cells. Diploid plants have two sets of chromosomes, those with more than two sets are called polyploids, e.g., tetraploids have four sets.

In Claytonia perfoliata and its close relatives, complex patterns of variation based on a chromosome set size of six were found, including distinctive populations with 12, 24, 36, 48 and even 60 chromosomes. Moreover, polyploid populations have broader ecological niches than the diploids from which they arise. Claytonia washingtoniana, a natural tetraploid hybrid between Claytonia sibirica and Claytonia perfoliata, is distributed in scattered localities from western Canada to northern California.

In addition to its chromosome characteristics, Claytonia perfoliata reproduces by selfing, which means that large quantities of seed, producing morphologically uniform offspring, can readily be produced. The mechanism of selfing involves the female and male parts of each flower coming into contact, often before the flowers are fully open.

Species with broad ecological niches, capable of producing large quantities of seed, have characteristics to be expected of successful weeds. Claytonia perfoliata was introduced into cultivation in Britain the 1790s, apparently from seeds collected by the Scottish plant collector Archibald Menzies in the northwestern North America. By the mid-nineteenth century it was a serious weed in Chelsea Physic Garden. Today, Claytonia perfoliata is a widespread, temperate weed, especially in cool, damp environments.

The name 'miner's lettuce' is a reference to the species' use as a minor food plant, during the 1850s California Gold Rush, for preventing scurvy. It may be eaten raw in salads or cooked like spinach.

Further reading

McIntyre PJ 2012. Cytogeography and genome size variation in the Claytonia perfoliata (Portulacaceae) polyploid complex. Annals of Botany 110: 1195-1203.

McIntyre PJ 2012. Polyploidy associated with altered and broader ecological niches in the Claytonia perfoliata (Portulacaceae) species complex. American Journal of Botany 99: 655-662.

Miller JM and Chambers KL 2006. Systematics of Claytonia (Portulacaceae). Systematic Botany Monographs 78: 1-236.

Stephen Harris