Racomitrium confessions: value of revisiting identifications



(This is an email message that I sent to bryo buddies several years ago; confessions that might give wise caution to young students of mosses.)

March 13, 2010

Well, yesterday was a humbling day in the lab. I have had to eat three determinations, ruining some good records.

First, I got around to looking into the packet of what I’d reported  was Racomitrium norrisii from the Olympic Peninsula. I made new sections, and they did not look at all like what I expected. The big fragments of chopped leaves in the mount didn’t even look like Racomitrium! …and they weren’t.

What I’d done previously is observe shoots with capsules, definitely Racomitrium capsules, and noted these plants had muticous leaves. “Probably R. aciculare, as correctly det. by Harthill,” I thought. There aren’t many of the capsule bearing shoots in the packet, so first time around I picked out a couple of vegetative shoots to make leaf mounts, something I do to avoid unnecessarily destroying fertile shoots. These leaves had obvious bistratose margins and the finely denticulate leaves characteristic of R. norrisii. So I reported that’s what I thought was at hand.

Well, it turns out this is a mixed collection. The vegetative shoots are Schistidium rivulare, the fertile shoots are Racomitrium aciculare. Harthill had gotten the Racomitrium specimen correctly identified, just included in his collection a lot of other stuff from the same rock. Sigh … Lesson: beware of mixed collections; be sure capsules belong to shoots you are studying.

Next, I re-examined a collection I’d called Racomitrium lawtoniae from California, from hot springs on Mt. Lassen. I’d always had a nagging in the back of my mind that something was wrong with that det. Just two weeks ago at CAS I came across several lovely specimens of R. lawtoniae that Jim Shevock gathered in British Columbia, in the company of Bill Buck and Judy Harpel. These were confirmed by Halina Bednarek-Ochyra. On the one hand, I was pleased to  see that all three collections were fertile and had right-handed twists to their setae, unique in the subgenus Ellipticodryptodon (=Bucklandiella). But, on the other hand, they were all very robust, with falcate leaves  characteristic of R. lawtoniae. The California collection I’d been unsure about was small, and had straight leaves. My re-examination came after having worked out R. affine from studies of other collections, and  this one proved to be that. I need to revise my keys to point out that the decurrent, hyaline hairpoints that characterize R. lawtoniae are also frequently present in R. affine, just on a smaller scale. There are other differences in costal anatomy and alar cells. Lesson: size characters are good characters; remember to always measure and record measurements.

Finally, I had my head slapped over two specimens I’d previously called Cynodontium strumulosum, one from North Cascades of Washington and one more recently from the Oregon Cascades. David Toren had keyed the latter (a R. Weiss collection) to Andreaea nivalis, something I’d not considered. David Toren is right. This species of Andreaea is a vegetative ringer for Cynodontium strumulosum and has fooled more prominent bryologists than me. I hadn’t paid attention to the costal anatomy even though I had good photographs of leaf sections. Lesson: pay attention to all data in hand.

So, I go forward more cautiously. I keep learning.

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