Agave schottii v. treleasei

[Gee.S]

Agave schottii v. treleasei (Toumey) Kearney & Peebles (1939)
Parviflorae

This appears to be an hybrid: A. schottii × A. chrysantha.

A. schottii v. trelease

schottii 002.JPG (134.27 KiB) Viewed 1929 times

[Gee.S]

ASDM 048.JPG (149.86 KiB) Viewed 1915 times

Arizona Sonoran Desert Museum

[Gee.S]

A_schottitrelease.pdf

(38.02 KiB) Downloaded 889 times

[Gee.S]

Habitat shots from south-central Arizona...

[Gee.S]

Today we ventured back toward the Santa Catalina Mountains in search of a very rare Agave. In our quest to find and document all 21 Arizona Agave taxa, we have been stuck on 19 for a long, long time, so it was really quite a thrill to push that number to 20 today, only one shy of our goal. We had made a run at our only remaining taxa, A. ×ajoensis, just over two weeks ago, but were unable to grab the ring. Our first attempt was documented here: Habitat: Organ Pipe National Monument. That may seem like a bit of a tangent, but that and the rare hybrid we found today are joined at the hip, by none other than HSG himself, who considered them the same species. It was subsequently determined that A. ×ajoensis = A. schottii × A. deserti v. simplex, while A. schottii v. treleasei = A. schottii × "A. chrysantha or A. palmeri". This ("A. chrysantha or A. palmeri") may seem like some sloppy bookkeeping, but the general area is inundated with an A. chrysantha population that butts up against A. palmeri, and may carry some A. palmeri genetic material.

I would just like to expound upon the taxon A. schottii var. treleasei, if I may. We've seen quite a lot of A. schottii across southern AZ by now, usually playing habitat hopscotch with A. palmeri, and never found a single example of A. schottii var. treleasei in these areas -- and our antennas were definitely up***. The only place we've found examples or encountered reports of this hybrid are at Santa Catalina, which is actually A. chrysantha territory, rather than A. palmeri, though certainly at the southern edge of chrysantha's range, and not far from the range of A. palmeri.

In the end, we should not have a named hybrid taxon with one established and two random parents. A. ×arizonica is A. toumeyana × A. chrysantha, not A. toumeyana × A. chrysantha or A. parryi. That would be ridiculous, and so is this. A. schottii var. treleasei cannot be A. schottii × "A. chrysantha or A. palmeri". It can only be one or the other, and in this case, it appears to be A. chrysantha. If there are A. schottii × A. palmeri hybrids scattered about somewhere***, that is either a different as yet unnamed hybrid, or better yet, just leave it unnamed.

Then we have to question the validity of taxonomic nomenclature. Gentry never saw this plant in habitat and named it based upon prior records and a Boyce Thompson collection:

This variety differs from the rest of the species with its larger, deep green, thicker, wider leaves (15-25 mm). Toumey reported type "in herb. J. W. Toumey" and living cotypes in gardens at the University of Arizona, Missouri Botanical Garden, and Dept. of Agriculture, Washington, D.C. I have seen none of these in the herbaria of the cited institutions. A drawing and two photos published with his description portray the plant, which is certainly closely allied to A. schottii. His type came from Castle Rock on the southern slope of the Catalina Mountains, Pima County, Arizona, at ca. 6,500 feet (2,000 m) elevation. A later collection from Organ Pipe National Monument, Pima Co., Ariz., was regarded by Kearney & Peebles as this variety. Further notes are given in the Exsiccatae. Good herbarium specimens are needed to better establish this taxon. Plants in the Boyce Thompson Southwestern Arboretum closely resemble the type clone.

Subsequently, Wendy Hodgson established the hybrid identity of the Organ Pipe population as A. schottii × A. deserti var. simplex and described a new taxon, A. ×ajoensis, in order to separate this group from the plants at Catalina, which Gentry considered conspecific. I spoke to Ms. Hodgson about this, and she had not understood which parent served as seed donor for this taxon, and I informed her that the donor is A. schottii, as we found large numbers of these hybrids at Organ Pipe, always growing in A. schottii patches. In any case, half the var. treleasei population to which Gentry referred has been taxonomically addressed and corrected, and it's high time the Catalina pop is corrected, as well. We know A. chrysantha and A. palmeri are diploid and that A. schottii is tetraploid, so a chromosome count on A. schottii var. treleasei that returns a triploid result should confirm its status as a hybrid. Assuming that result, the name should be revised to A. ×treleasei and described as a naturally occurring hybrid of A. schottii × A. chrysantha.


*** We did find a possible A. schottii × A. palmeri population in Cochise County. Greg Starr leans toward that ID for these plants, while Wendy Hodgson and I lean toward A. schottii × A. parryi. In the end, we don't really know. If we're lucky, we may be able to sort that out in the near future by examining fresh blooms. Even if this bunch does pan out as A. schottii × A. palmeri, that in no way diminishes the case being made here, since the Cochise population appears distinct from A. schottii var. treleasei, and instead looks exactly like A. ×ajoensis.

[Gee.S]

Agave schottii var. treleasei

DBG 068.JPG (221.99 KiB) Viewed 1615 times

[Gee.S]

Bloom shot, w/aphids galore!

A. schottii var. treleasei

Seedlings 007.JPG (53.69 KiB) Viewed 1258 times

[Gafoto]

Surprised to see this plant today in the Santa Catalina mountains. It's making the very dubious decision to flower in December but fortunately it's got another head as backup.

Tre1.jpg (914.32 KiB) Viewed 235 times

tre2.jpg (481.05 KiB) Viewed 235 times

tre3.jpg (689.06 KiB) Viewed 235 times

tre4.jpg (273.4 KiB) Viewed 235 times