How to differentiate Vicia cracca and Vicia villosa

Vicia cracca and Vicia villosa are widespread, coast to coast, non-native vetch species found in the United States and Canada. They are similar in appearance, most notably for their dense, one-sided clusters of purple flowers. Differentiating the two requires a close look at the flowers (NOT the presence/absence of hairs!). Since the iNat computer vision still seems to struggle with these two, I will attempt to explain the best characteristics to look at in V. cracca and V. villosa.

TL:DR; Quick Summary:
V. cracca Banner petal is equal in length to the claw of the flower. The flower stem attaches to very end of the flower. Sepal lobes are short and triangular.
V. villosa Banner petal is half the length of the claw. The end of the flower is swollen, giving the appearance of the stem attaching to the bottom of the flower. Sepal lobes are long and thin.

This illustration is helpful to see the differences in the flowers: https://www.inaturalist.org/photos/15140861?size=large
V. cracca is pictured at the top and right, V. villosa at the bottom and left.

FLOWER PROPORTION:
V. cracca: Length of the upright portion of the banner petal equals the length of the claw.
V. villosa: Upright portion of the banner petal is half the length of the claw.
Banner petal: on a legume, this is the petal on the top of the flower. Viewing the flower from the front, this is the petal that stands upright.
Claw: For our purposes, the claw is the back half of the flower, the tubular or cylindrical half of the flower.
Your eye will be able to pick up the differences in proportion. V. cracca has a proportionally large banner, giving it a squared off appearance from the side. V. villosa has a proportionally small banner, giving it a long narrow profile.

FLOWER BASE:
V. cracca: Flower stem attaches at the very end of a flower.
V. villosa: The end of the flower is gibbous, or swollen. This will give the appearance of the stem attaching from underneath the flower instead of at the end. This feature is best viewed from the side of the flower (see linked illustration above). The end of the flower is a rounded bump that extends past the stem in sideview.

SEPALS:
V. cracca: Sepal lobes are short and triangular
V. villosa: Lower sepal lobes are long, narrow, and thin.

RANGE:
V. cracca: Generally concentrated around the U.S./Canada border (especially the coasts), New England area
V. villosa: Widespread in continental U.S. Found in interior and southern U.S. more so than V. cracca.
Note: The ranges overlap considerably, this is just a generalization.

HAIRS ON STEM AND LEAVES:
V. cracca: May or may not have appressed hairs (lie flat to surface)
V. villosa: May or may not have spreading hairs (hairs that stand upright or spread)
Contrary to popular belief, the presence or absence of hairs on the stem and leaves does not mean one species or the other. Both species are variable in overall hairiness. Rather, look at whether the hairs lie flat or stand up. Use this as a clue, not a diagnostic trait.

LEAVES/STEM:
Very similar and probably not reliable enough to base an ID off of, at least not here on iNat without being able to measure things. My hypothesis is V. cracca typically has more leaflets that are more densely packed together and more likely to be opposite of one another. In any case, base your ID off flowers whenever possible.

Publicado por csledge csledge, 30 de octubre de 2021

Comentarios

Great summary - thanks for doing this work and sharing it

Publicado por rnheld hace 11 meses (Marca)

This is very helpful. I've seen myself that hairiness can be pretty variable, especially on villosa, so it's good to see other characteristics are diagnostic, maybe more so. I think I have images illustrating these flower differences and I'll be updating our own species accounts accordingly. Thank you!

Publicado por mnwildflowers hace 8 meses (Marca)

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