Identificaciones de plantsarecool

[Photos submitted as part of a botanical survey for Rocks Ranch / Santa Cruz Land Trust]

Plant ID Diary/Blog

This plant was found growing in open grassland (grazed long-term by cattle) near a low, erosion-rounded rock outcrop covered with lichen...typical of the scattered hillside outcrops found at Rocks Ranch, and giving the place its name.

For better or worse, I usually avoid spending time IDing weedy introduced species like this, preferring to focus on the native flora which I find more interesting and aesthetically pleasing. But this one somehow caught my fancy...being somewhat small (about 1' tall); seemingly well-behaved (the only one in the vicinity); and with tidy, well-spaced, simple, mildly-dentate cauline leaves (rather than the rank, irregularly-lobed leaves typical of many weedy mustards). I thought: "I need to learn more about all those weedy mustards, and this might be a nice one to try to ID". How was I to know that the qualities that drew me in were largely the result of it being a depauperate individual? And that...together with a lack of fully-mature fruit...would make IDing this trickier than I initially expected? And, of course, there were hiccups arising from the ever-present "character variability" lurking within so many biological taxa (the bain of us seekers of a tidy taxomomic heaven ;-).

The first resource I turned to was the Jepson eFlora Brassicaceae key, though after encountering various difficulties of interpretation, I soon consulted the FNA Brassicaceae key...hoping the more technical and complete style there might help clarify some of the ambiguities I was running into. It turns out both treatments were written by the same author, and the sequential structure of the keys and characters used are very similar...so studying both gives a good sense of the impact arising from the different philosophical & format sensibilities imposed on authors by the editorial committees for those two references. On the one hand, the Jepson Manual/eFlora is based on a single volume tome covering CA only, and is intended to be accessible to the (persevering!) layperson. The FNA, on the other hand, covers most of North America (i.e. north of Mexico), is unabashedly technical, and can be challenging to wade through even for highly-trained botanists...and it comprises 26 volumes (+ 2 more for mosses).

Anyway, after reviewing some terminology (and fortunately already being familiar with more), I was able to navigate both keys nearly to their ends...arriving penultimately at a decision between two candidate genera: the type genus Brassica, or the genus Sinapis. The following sequence of key characters, discernible in the 3 photos, were used:

• hairs simple (= unbranched) or lacking (they're very sparse here...mainly near the base of the plant); cauline (= stem) leaves present, not lobed or clasping (leading to "Group 2" in both keys);
• flowers radial; stamens 6; ovaries & young fruit linear (i.e. "siliques" that are much longer than wide);
• stem leaves simple; multicellular stalked-glands lacking;
• stamens tetradynamous (= 4 stamens long, in two equal-size opposite pairs & 2 stamens short, in a lateral pair);
• petals not dark-veined; cauline leaves dentate; petals yellow; inflorescence not bracted;
• ovary, young fruit 2-segmented (= a shorter portion with 2 thin, lateral sheathing "valves", and a longer "beak" beyond that...this character is subtle, but can be discerned by scrutinizing the 2nd photo at full-size);

From there the choices are:

• Sepals generally erect to ascending; fruit valves 1-veined; stigma entire to ± 2-lobed; seed spheric to ovoid .....Brassica
• Sepals spreading to reflexed; fruit valves 3–7-veined; stigma 2-lobed; seeds spheric ......Sinapis

This is where the ambiguities really begin to kick-in. In the 3rd photo, the sepals are clearly ascending...suggesting Brassica from the key; while the fruits are too immature to discern the number of valve veins. The stigmas appears ± 2-lobed, but that character and those of the seeds are not diagnostic among our two options.

Proceeding to the Brassica key, neither choice at the 1st couplet seems good here: i.e. the bases of the cauline leaves visible in the 1st photo are neither "lobed or clasping" nor particularly "tapered"...though if I had to choose I'd go with the 2nd lead there. For the choices beyond there, I'd go with: 4') pedicels in fruit ascending; 5') leaves ± glabrous; and 6') fruit stalk above receptable 0...leading to a tentative species candidate of B. juncea. But note that at couplet 5) both leads indicate the presence of lateral lobe pairs...and there appear to be none on the leaves of this plant. That could possibly be due to the depauperate state of this plant and/or variation...but it also more strongly compels us to investigate the alternative option of Sinapis !

[Aside: One might (rightfully!) question why I went with the choice 4') rather than 4): "pedicels erect, appressed to the inflorescence axis"...which appears to be a better fit here? I did so because, after checking the descriprion of B. nigra, I found it's described as a much-branched and larger plant...with basal AND lower cauline leave conspicuously lyrate-pinnatifid. The few basal leaves here have dropped (note the leaf scars at the base of the plant)...but I believe B. nigra would still exhibit some lobing in at least the lower leaves visible here...and there is none. When keying, one is navigating a device meant to suggest an optimal ID candidate, based on the of the author's best attempt to synthesize knowledge of the taxa into a dichotomous-choice decision-tree. But that can be a very hard goal to effectively achieve, given the vast amount of diversity & variability often present among the taxa being considered. And authors are human, and thus capable of oversight & error in composing a key...so it's good to carefully reconcile the result of a keying process with detailed descriptions of the resulting candidates!]

So next I proceeded to the Sinapis key, which thankfully has just one couplet...though things are still ambiguous here. On the one hand, the first choice, which leads to S. alba, indicates its fruits are "long-bristly" (doesn't fit here) and also have the distal fruit segment ≥ the proximal one (which does fit here). On the other hand, the second choice, leading to S. arvensis, indicates its fruits are ± glabrous (fits!) but have the distal segment much shorter than the proximal segment (doesn't fit!).

I think any reasonable person will conclude this must be a hybrid between S. alba and S. arvensis...one perhaps well-referred to as S. albarvensis? ;-)

Then again...the more sober, less playful, taxonomists among us may opt for an alternate explanation: i.e. that the fruits are not mature here, and the "beak" (= distal portion) may yet grow and become much longer than the proximal "valved" portion of the fruit. I am a very sober taxonomist who strictly abstains from playfulness...so I'm leaning towards S. arvensis.

Checking out the line drawings for S. alba and S. arvensis on the Jepson eFlora page for S. arvensis...and the photos on this DiscoverLife page... strengthens my zeal for S. arvensis. The truly dedicated student would still want to investigate the B. juncea option...to further ascertain whether it merits elimination (or perhaps adoption). As they say in the math books: "That is left, herein, as an exercise for the diligent reader".

[PS: An adherent of the "Wizard of Oz" school of thought may have simply asked iNat's AI image anaylsis routine for its ID suggestion here. After all was said and done above, I tried that...and somewhat amazingly (and in some ways alarmingly) it provided "Brassicaceae" and "Sinapis arvensis" as the first two options. That modus operandi seemed to work here, and often does for other ID's...so: Why bother with studying the plants, the botanical subject matter...the ideas, terminology, fine nuances, endless details, etc.?? The simple answer seems a no-brainer...just ask the Wizard of Oz to get the ID, and then you can spend all the time you saved doing other things! Solutions to the {far more nuanced and important} problems posed by the above question are also left, herein, as an exercise for the diligent reader ;-]

NMH956

Montane coniferous forest. Open understory with few shrubs. Substrate duff, decomposed granite, and large granitic boulders. Mostly flat, with slight slope facing east. Next to dirt trail, and stream filled with Prunus sp. and Salix sp. w/ Pinus jeffreyi, Pinus lambertiana, Abies magnifica var. shastensis, Hosackia oblongifolia var. oblongifolia, Chrysolepis sempervirens, Prunus sp., Salix sp.