August 29, 2020

Two Koelreuteria species and their seedlings as weeds

Comparison of Adult Trees

Koelreuteria paniculata blooms in early summer (June) and by August is already in fruit. The leaves are once-compound, also called pinnate. Leaflet margins have some notches, with random variation in how deep each notch goes. The seeds are contained in a closed, inflated papery covering which is boxy on top but comes to a point at the bottom. At least on our tree these papery fruits go from pale green to brown without blushing pink.





Koelreuteria bipinnata, as the name suggests, has bipinnate leaves, aka twice compound. Each leaf terminates in a fork. Margins are serrate. The trees bloom in late summer (August) and the fruit will be blushing pink in the fall. I'll have to photograph those when they come. The papery fruit are a different shape than those K. paniculata, more of a winged shape than inflated, and blunt on the bottom.


At this point you might be thinking, what about Koelreuteria elegans? K. elegans is extremely similar to bipinnata, and unfortunately I don't have a specimen to examine. One source told me K. elegans is evergreen while K. bipinnata is deciduous, and another suggested slight differences in leaflet shape and venation. Sounds difficult.

Comparison of Seedlings
Let me start off by noting, K. bipinnata is extremely more weedy than K. paniculata, at least at my location in Southern California. Left alone, the ground under a K. bipinnata tree becomes a carpet of competing seedlings. For K. paniculata, even when I stood directly under the adult tree, the vast majority of seedlings around were from the K. bipinnata tree up the hill! Even if you don't have a tree, if you've ever received wood chip mulch from an arborist company, any K. bipinnata seeds in it will make your life miserable. They are easiest to kill when under a foot tall. Very small ones can be scuffled with a hoe, and slightly bigger ones pulled by hand. After they get too big, the roots are too strong.


A mess of K. bipinnata seedlings

So here's were things get confusing. K. bipinnata juvenile foliage doesn't look like its adult foliage, and unfortunately looks very much like K. paniculata adult foliage. At younger stages, K. bipinnata leaflets are incised in variable and random scallops. On these recent sprouts, the leaves are small enough to make it very difficult to judge whether the leaf is bipinnate or merely pinnate. Each leaf terminates in a leaflet rather than a fork, even when the seedling has reached a reasonable size.


A newly sprouted K. bipinnata whose leaves are so small the bipinnate form is not clear.

Slightly bigger, but still unclear!

These are old enough to be more bipinnate.

A leaf from the group above.

A group over a foot tall.

A leaf from the group above.

A seedling almost a meter tall, finally showing obvious bipinnate leaves with serrated margins, but still showing the leaf groups terminating in a leaflet.

A leaf from that seedling.

So now, some K. paniculata seedlings. You'll notice the foliage is still confusing regarding whether it is pinnate or bipinnate. Sometimes you'll catch little "wings" of leaf blade along the midrib, especially towards the terminal end.



And now for a little comparison. All the K. paniculata seedlings I found had their leaves much closer together along the stem, giving them more of a rosette shape. I can't tell if this is a real characteristic or an environmental factor. So here we have K. paniculata LEFT and K. bipinnata RIGHT, with the center photo showing both.

Here they are again, just bigger. Starting with K. paniculata and ending with K. bipinnata.


Posted on August 29, 2020 21:18 by arboretum_amy arboretum_amy | 0 comments | Leave a comment

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