For the fourth entry in the series on mimicry and deception, Taisha writes about a plant found throughout much of the world:
Vicia sativa subsp. nigra or black-pod vetch (one of many common names), was photographerd here by frequent BPotD contributor Robert Klips (aka Orthotrichum@Flickr | via the BPotD Flickr Pool). Thanks Robert!
Today’s taxon doesn’t use mimicry for the purpose of pollination, but its mimicry does contribute to its reproductive success. This fabaceous taxon uses Vavilovian mimicry (or weed mimicry or crop mimicry), where a weedy taxon takes on one or more of the attributes of a domesticated crop taxon through unintentional artificial (or human-induced) selection. Vavilovian mimicry is named after Nikolai Vavilov, a Russian plant geneticist who first observed and described this phenomenon in the 1920s.
In the case of black-pod vetch, some of the seeds mimic lentil seeds in shape and mass. Black-pod vetch is often found growing in lentil crops, and when the lentils are harvested, it’s not uncommon that mature vetch plants are processed by the machinery along with the lentils. Some vetch individuals have a recessive genetic mutation resulting in flattened seeds, strongly resembling those of the lentil. During the process of seed cleaning, the vetch seeds are unintentionally sorted with the lentils and later replanted, increasing the success of that particular genetic lineage (see: Erskine, W. et al. 1994. Mimicry of lentil and the domestication of vetch and grass pea. Economic Botany. 48(3):326-332).
Vavilovian mimicry can also occur vegetatively, as in barnyard grass (Echinochloa crus-galli var. oryzicola). The barnyard grass camouflages itself amongst crops of cultivated rice (Oryza sativa) by strongly resembling the young rice plants. One of the few distinctions between the two is a small ligule that can be found on the rice plants. However, because it requires effort to search for the ligule, it is inefficient to remove the barnyard grass by hand weeding. Those that do stand out for some readily apparent reason are weeded out, so there is an artificial selection pressure to resemble the rice plant at that stage in its life cycle.
This form of mimicry can have positive effects (from a human agricultural perspective). Some species that were once considered weeds are now important crop species. For example, the progenitors of rye (Secale cereale) and oat (Avena sativa and ilk) were once considered weeds growing amongst wheat (Triticum spp.). However, being exposed to similar selection pressures, these ancestors of modern rye and oat crops developed domesticated traits such as large seeds, rigid panicles, and non-shattering qualities, thus making them suitable for growing as cereal crops. These once-weed crops were termed secondary crops by Vavilov (see: Barrett. S. 1983. Crop mimicry in weeds. Economic Botany. 37(3): 255-282).