Castilleja arvensis Schltdl. & Cham.
A mildly weedy species, Castilleja arvensis is one of the few annuals in Castilleja outside of the primarily Californian group formerly classified in Orthocarpus and is unique in the Section Euchroma both in its weedy habit and its annual duration and minute seeds. It is found throughout nearly all of Mexico, Central America and South America and has a wide elevational range, occurring from foothills to the paramo in the Andes Mountains . While it occurs as far north as Tamaulipus, Mexico, to the best of my knowledge it has not been recorded north of the Mexico border in North America. It is found in the U.S. only in Hawaii. As a weed it is pretty cool and just sort of hangs out at the edges between humanity and the wild places, including early colonization of recent lava fields in Hawaii. As far as I have seen, it does not create infestations but occurs in much the same manner as a humble but adaptable native species. Does anyone in Hawaii have different experiences, where it is more problematic? It has also been recorded in the Carribean region, at least on the island of Haiti, as well as in the Galapagos Islands, but my knowledge of those populations is fragmentary.

Most populations are predominantly or entirely red-bracted, but a small population near the Hilo Airport when I first observed it in 1997 was quite varied in color, something I've not seen in any of the other populations of this species I've encountered. Two years later I could only find a few, typically reddish-bracted individuals in the same location. This set includes a number of photos of the unusual white to pink-bracted plants.

It's come to my attention that this species is listed in the recently posted "The Plant List", as a synonym of the somewhat related endemic of eastern and southern Mexico, Castilleja scorzonerifolia Kunth, but this is clearly wrong. Please see for yourself by comparing these photos with my set of true C. scorzonerifolia:

The two species are separable on numerous points of morphology and habit, and this seemingly unpublished synonymy included on The Plant List demonstrates a cursory and superficial knowledge of the plants in this genus on the part of whoever so listed it (the list is posted without attribution). They should have asked me, because I already have a better list and the documentation to support and manifest it. In truth, the species most similar to and easily confused with C. arvensis is not C. scorzonerifolia but rather Castilleja nervata Eastw., a perennial, non-weedy endemic primarily of the western cordilleras of Mexico. I've posted a few of the many photos I've taken of C. nervata already (those from Cochise Co., AZ), so you can see that species here as well:

Many more of C. nervata from Mexico will be posted here in the future.
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