False Mountain Willow

From reading up on false mountain willow (Salix pseudomonticola) on the MN rare species guide, I knew it occurred along the St. Louis River somewhere. I figured Jay Cooke was probably the most likely place, after all public land is much easier for botanists to survey than getting permission on private. So, I followed Joe’s advice, look for a distinguishing feature on the landscape and then zoom in and find a distinguishing feature on that feature and so on. Obviously the St. Louis is a big distinguishing feature, by far the largest river in the area, that feeds into the largest lake on the continent. Looking at the satellite map, I saw a large section of waterfall with three large sandbars in the river right after, and what looked like a steep slope along the edge of the river; three distinguishing characteristics in a small area. That had to be the spot! Sure enough after trekking out there I found the willow after about 30 minutes of searching. Willows are usually pretty hard to ID, but false mountain willow has a few pretty distinguishing characteristics: large, persistent stipules; relitevly large leaves; hairy, yellow young stems; hairy, red new leaves; red petioles/midveins, and a shrub form reaching up to 11 ft. tall. There are many more characteristics but at that point there’s not much else that looks like it, the closest probably being heart-leaved willow. This species is listed as a state special concern species. It is more common, although still quite rare in the northwest of the state where it occurs in wet prairies. That range is continuous with its population in Canada. The northeast population along the St. Louis is disjunct. It occurs on a steep clayey bank. 

False mountain willow (Salix pseudomonticola)
State Special Concern Species
Notice the large stipules and leaves

Notice the hairy red petioles and hairy yellow young stems

While in the area I found an abundance of other willows. 

Balsam willow (Salix pyrifolia)

Sandbar willow (Salix interior)

Heart-leaved willow (Salix eriocephala)

Bebb’s willow (Salix bebbiana)

Crack willow (Salix x fragilis)
Invasive

Willows are keystone species in this region supporting a wide variety of insects, especially as a lepidopteran larval host plant and a host plant for specialist bees. There are also many gall midges that use willows as a host. I saw various galls on many of the willows, but wasn’t looking out for caterpillars, although I’m sure there were quite a few there. MN is home to many species of willow, some common and some rare, some have a wide habitat range and some a very narrow one. I wonder what role each species plays in the ecosystem at large. Do they all contribute equally or are some species better in their role as host plant, photosynthesizer, shelter provider, soil stabilizer…?

Willow pinecone gall midge (Rabdophaga strobiloides) on balsam willow

Potato gall midge (Rabdophaga salicisbatatus) on heart-leaved willow

Willow redgall sawfly (Euura proxima) on crack willow

Willow bead gall mite (Aculus tetanothrix) on false mountain willow

I’m also curious to learn more about crack willow, I know it is considered as a non-native invasive species. Does it support insects in the same or similar way as the natives. Most willows are pretty competitive and can form small monocultures. What species does crack willow outcompete, mostly other native willows, or many other species as well?





















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