Notes on Linum rigidum & Linum berlandieri with a focus on Central Texas
"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint, it's more like a big ball of wibbly wobbly, timey-wimey stuff."
The situation with Linum rigidum and Linum berlandieri is a little wibbly wobbly with regards to differentiation and timey-wimey in regards to species circumscription. These species are closely related; L. berlandieri has been grouped under L. rigidum at certain points in time by certain authors (as L. rigidum var. berlandieri). Currently the two are treated as separate species but the process of distinguishing them is somewhat complicated as most of the distinguishing characters are not clear-cut between the two. Nonetheless I will try my best to cut down both the wibbly-wobbly and the timey-wimey using information from FNA (last edited in 2020), FNCT (1999), and other publications.
FNA = Flora of North America, page on Linum last updated 2020 (website: http://floranorthamerica.org/)
FNCT = Shinners and Mahlers Illustrated Flora of North Central Texas, 1999 (online PDF: https://fwbg.org/research/brit-press/illustrated-flora-of-north-central-texas-online/) - pages 788-792
MVPT = Manual of the Vascular Plants of Texas, 1970 - pages 897-899
Current Species Circumscription
(According to FNA)
Linum rigidum Pursh
With 2 varieties:
Linum rigidum Pursh var. rigidum
Linum rigidum var. simulans C. M. Rogers
Only var. rigidum occurs in Texas.
Linum berlandieri Hooker
Synonym: Linum rigidum var. berlandieri (Hooker) Torrey & A. Gray
With 2 varieties:
Linum berlandieri Hooker var. berlandieri - widespread in Texas except W. Texas, spreading north to Nebraska, east to Louisiana and Arkansas, and west to New Mexico.
Linum berlandieri var. filifolium (Shinners) C.M. Rogers (same as Linum rigidum var. filifolium Shinners) - Central? and W. Texas, and Mexico (Coahuila)
(Distribution of varieties from USDA Plants Database, FNA, and MVPT)
In Central Texas, L. rigidum var rigidum and L. berlandieri var. berlandieri are most relevant. L. berlandieri var. filifolium may also be present, though this is only mentioned in FNA.
Distribution
Here are the BONAP distributions for both species from 2014:
L. rigidum
http://bonap.net/MapGallery/County/Linum%20rigidum.png
L. berlandieri
http://bonap.net/MapGallery/County/Linum%20berlandieri.png
Based on this, it would seem that in most of Texas, L. berlandieri is significantly more widespread than L. rigidum. The USDA Plants Database maps are similar (zoom in to show county-level distribution):
L. rigidum
https://plants.sc.egov.usda.gov/home/plantProfile?symbol=LIRI
L. berlandieri
https://plants.sc.egov.usda.gov/home/plantProfile?symbol=LIBE2
Based on both maps, L. rigidum as currently defined is nonexistent in Central Texas. A quick check on SEInet, however, does show L. rigidum in Central Texas. Based on this, it seems better to assume that L. berlandieri is more common than L. rigidum in Central Texas—how much more common, I do not know.
Identification
Fruiting Capsules
This appears to be the only straightforward method to distinguish these two species (supported in MVPT, FNCT, and FNA).
L. rigidum has capsules which are elliptic (oval) in shape. The base of the capsule is rounded.
L. berlandieri has capsules which lean closer towards a triangular shape - ovoid (egg-shaped) to triangular-ovoid. The base of the capsule tapers abruptly to form a flattened base.
A closeup illustration of Linum rigidum capsule shape can be found on page 791 of FNCT (as Linum rigidum var. rigidum). You can also find the same illustration at the USDA Plants page.
Identified as Linum rigidum, though I suspect it might be Linum compactum. Regardless of its identity, though, this image displays the elliptical capsule shape very well. From https://www.inaturalist.org/observations/181008072
Linum berlandieri capsules. From https://www.inaturalist.org/observations/163254484
Another useful (though slightly less-straightforward) character is the thickness of the capsule walls.
L. rigidum has translucent capsule walls, "so thin that the dark seeds can be seen through them," per FNA.
L. berlandieri has thick, opaque capsule walls—or at least for Linum berlandieri var. berlandieri.
Linum berlandieri var. filifolium (which may or may not occur in Central Texas) apparently has thin-walled, transluscent capsules, per FNA. It is not said whether the capsule walls are thinner than Linum rigidum. However, this variety is very unique in that it contains greyish or purplish-colored sepals and a black stigma, which neither of the other species contain.
To be continued?
Comments
Yes, apparently I like Doctor Who now.
Separate note: L. hudsonoides and L. imbricatum can be separated from L. rigidum and L. berlandieri from the closely-appressed distal leaves (distal = away from point of attachment, in this case the side further from the ground).
Thank you so much for this. All your journal posts are much appreciated!
the issue of a pedestrian ID for L. rigidum and L. berlandieri are smiliar to ID of Corydalis aurea and Corydalis micrantha, with photos of the bloom and plant only, the appropriate ID may be at the genus level
@ronstephens yes, I've always considered those plants together as general group (L. rigidum/L. berlandieri), since most observations would be difficult to identify to either species. I compiled this information mainly for @atlasmira since she is collecting seeds and was interested in a way to distinguish them; naturally, fruit morphology works quite well for that. There is also the use of stipular glands as a distinguishing feature as well, but I haven't spent much time on that and it is not as consistent compared to the fruit.
got it thanks!
After taking a stab at L. hudsonioides and L. imbricatum this year, I had hoped to also look at L. berlandieri and L. rigidum, but I have not seen any this year, probably due to greatly reduced field time. The characteristic differences in so many of the Linums, including the two here, are often so subtle that I doubt I could tell most of them apart, and in many cases I would probably need a scope to do so.
@rymcdaniel yes, I found it quite challenging. I have reviewed a fair bit of literature here but haven't applied any of the information to plants in the field. I still have not located stipular glands on plants (which is a distinguishing trait)—or more specifically, I can't tell if they are present or absent, or what they even look like. My guess is that they are very small and impossible to see without a good loupe or a scope. As least the fruit morphology seems promising, though I haven't looked at any plants to put the knowledge in practice. I likely will not be anytime soon as I will be busy working in IL for the next two months.
Update 13 January 2024: Added somes images of fruit to post to show differences in fruiting capsule shape. Also found that the illustration in FNCT can also be found on the USDA plants website, so I linked that in too.
It would be nice if more people took pictures of the fruit for these plants. I will probably be out next year looking for these and taking images of fruiting capsules, as well as searching for the elusive "stipular glands" :)
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