Ivesia tweedyi (non-technical)


Ivesia tweedyi and the more widespread Ivesia gordonii are very similar species with ranges that overlap in the Washington Cascades and northern Idaho. Both are quite small with yellow flowers and dark green leaves in distinctive cylindrical bundles that look rather like squirrel tails or fat pipe cleaners (technically pinnate compound dissected leaves). All the leaf bundles radiate from a single point at ground level. They are both found on high mountains in sun usually in rocky soil and may be locally very abundant, with I. gordonii ranging much farther south and east than I. tweedyi.

In general appearance, both look very much like this observation: https://www.inaturalist.org/observations/28320251

I. tweedyi is distinguishable in photographs from I. gordonii mostly by subtle features of the flower: tweedyi has yellow petals that are longer than the greenish triangular sepals (https://www.inaturalist.org/observations/125949005), whereas gordonii has petals that are similar in length or shorter than the sepals (https://www.inaturalist.org/observations/822050). The difference is not always as obvious as in those two photos, in which case it is better to use a genus level identification. The base of the tweedyi flower is described as being shallower than gordonii (bowl rather than cone shaped) but this difference is not as readily visible in photos unless there is a careful side shot of the flower. In the field you may be able to tell by eye: the tweedyi flower has a flatter shape whereas gordonii has a deeper depression at the center.

Finally, though their general ranges overlap, the two species seem to occupy different soil types (or microclimates or something) so if your observation is very near a previous one that is well identified, then it is probably the same species. Ivesia tweedyi but not gordonii is well adapted to serpentine rock and soil, but tweedyi is also sometimes found off of serpentine especially near Mount Rainier and in the Mount Aix range just east of Rainier.

You will need a good picture of the flower to tell them apart, preferably a closeup.

[You are welcome to improve this post by sending me an iNaturalist email, but I am disabling direct comments because this is intended as a brief guide, not a discussion.]

Publicado el 18 de julio de 2022 22:11 por jhorthos jhorthos