The Biologist Is In: A Pretty Little Weed

Tuesday, January 17, 2017

A Pretty Little Weed

One of my favorite roadside wild-flowers is the invasive Eurasian weed Lotus corniculatus (Bird's Foot Trefoil). It is almost always found in a bright yellow, but I've been keeping a look out for forms with other colors. I occasionally find plants with enhanced red/orange streaking, but never as intense as the one in the photo below. I did once find plants with distinctly [pale-]orange flowers in a southern California ocean-side park. (Unfortunately there were no seed pods to be found.)

I found the following representative images from various sources online.

L. corniculatus in yellow.

L. corniculatus in orange.

Cluster of small yellow flowers with red marks.

L. corniculatus with red streaks.

I'm really quite surprised I haven't found any evidence for a white flowered variation. All it would take is a single mutation to inactivate one of many genes involved in the early steps of the pigment pathway, which should make it a pretty easy variation to arise. Maybe white flowers don't attract whatever pollinates this species and so the trait would rapidly die out after being formed.

The plant family containing this species (Fabaceae) has flowers covering the whole spectrum of flower colors. Reds, blues, yellows, and whites are all common. These colorful relatives suggests there may be the genetic potential for more color diversity within this species, even though they are not yet apparent.

Additional interesting flower color genes can be found in close relatives. If we're very lucky, maybe these related species could cross to L. corniculatus. Improving the floral characteristics of a common weed isn't the sort of project that is going to get much research funding, so there might not be much information available about the possibility of inter-species crosses within the genus. For now, lets just make pretend that we can do these crosses and have a look at what genetics might be available in the genus Lotus.

Cluster of small yellow and white flowers, next to cluster of narrow elongated seed pods.

L. pinnatus

The closely related L. pinnatus (Bog Bird's Foot Trefoil) is an uncommon species found in western Canada and the USA. Its lower two petals are splayed open and a bright white color. These flower traits suggest this species would be interesting to cross to the more common weedy species. L. pinnatus grows as a sprawling plant in boggy wetlands.

This dramatically different lifestyle of this species means there would be many non-floral traits that would need to be cleaned up via back-crossing to L. corniculatus if we wanted to maintain the growth form of the original weed. I like the weed's growth habit, so this would be a goal for me.

Cluster of small yellow and purple flowers.

L. formosissimus

A similar species to L. pinnatus is L. formosissimus (Seaside Bird's Foot Trefoil). This one has the same fancy flower shape, but comes in a greater diversity of color forms.

L. tetragonolobus

Another close relative is L. tetragonolobus (Asparagus Pea). This species produces edible (and tasty) winged seed pods. The flowers are a brilliant scarlet-red, which would be a lovely trait to bring into the mix. The plant grows as a low mound, much like L. corniculatus, so I wouldn't need to worry about cleaning up the genetics of a cross so much. They also seem to come in versions with yellow flowers. The traits that result in this species having tasty pods might also be a cool thing to select for in any hybridization projects. (Maybe I'll just grow this species in the garden anyhow.)

Some more research into this group reveals there is abundant information about hybridization between species. The reason is that the various species are common forage plants in pasture. Any species impacting agriculture will have a lot of research done on it.

Some of the hybrids I can find information for:

L. corniculatus x L. tenuis
L. uliginosus x L. tenuis
L. corniculatus x L. stepposus

Unfortunately, none of these species have much of anything going on for interesting flower colors. That these crosses work, however, suggests other crosses in the genus might also work. Knowing something about how many chromosomes are found in species of the genus might help sort out what crosses have a better chance of working, but it really comes down to simply trying the crosses and seeing what happens.

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