Symphyotrichum subulatum "complex"

This is something I wrote on an observation from San Antonio at this link: It probably can apply to anywhere, with modification.

There are (or were) five varieties of S. subulatum (see descriptions at POWO has recently (in the last few months) synonymized S. subulatum var. ligulatum to S. divaricatum and S. subulatum var. parviflorum to S. expansum (the latter based on 2018 Catalogue of Life circumscription). The December 2021 Catalogue of Life release now synonymizes S. expansum to S. parviforum, which takes nomenclatural precidence because of the timeline in which the basionyms were described. I expect POWO will update to that eventually (probably sometime this year).

Most iNat observations of the varieties of S. subulatum are only at the species level. However, the varieties are quite different in characteristics, and most of their ranges do not overlap. These are likely two of the reasons for the change in acceptance of some (and probably later more) of the varieties back to the species level as proposed by Guy L. Nesom in the 1990s. So, an ID of S. subulatum at the species level can somewhat confidently be honed down to varietal level.

In Texas, the most common at the former varietal level is S. subulatum var. ligulatum (now S. divaricatum), followed by S. s. var. parviflorum (now S. expansum or S. parviforum, depending on the circumscription as I discussed above). The autonym is S. s. var. subulatum, or the actual equivalent of the species, and the USDA PLANTS database shows that it only has a presence in Texas in Chambers and Orange counties. The other two varieties, S. s. var. squamatum (circumstribed to by some as S. squamatum) and S. s. var. elongatum (circumscribed to by some as S. bahamense) are not native to Texas and have a very different native range. However, S. s. var. squamatum, although a native South American species, does have an introduced presence in a few southern US states, including Texas, according to POWO and the USDA PLANTS database. In Texas, var. ligulatum (now S. divaricatum) and var. parviflorum (now S. expansum or S. parviforum) have mostly non-overlapping ranges, with the latter solely in the southwestern-most counties. In San Antonio, only S. divaricatum is present according to USDA PLANTS database (unless of course the introduced S. s. var. squamatum is there, but there is no data available on the county-level for the introduced, or I haven’t found it yet).

What I am working on is trying to sort out the species-level S. subulatum identifications into the appropriate varieties, or new species names where relevant. This has to be done manually rather than with an automatic taxon name swap because, as I said, most of the observations are at the species rather than varietal level.

Regarding characteristics, these are also quite different among the varieties. From the FNA link I gave above (including drilling in to the varieties), here are a few of the differences as applied to the observation I linked to, above (

S. subulatum var. subulatum has 16-30 ray florets in 2 series that are white and that dry white or lavender in 0-1 outward-curling coils. Characteristics do not match the observation. Add to it the lack of presence in the area, and I ruled this out.

S. subulatum var. squamatum (S. squamatum), 21-28(-38) ray florets in 2-(3) series, white, drying white or lavender with INWARD curls but rarely coiling. Introduced in Texas. Characteristics do not match the observation. I ruled this out.

S. subulatum var. elongatum (S. bahamense), 30-54 ray florets in 2-3 series, pink to lavender and drying in 2-3-(4) outward-curling coils. Characteristics do not match the observation. Far southeastern US species including the Caribbean. No recorded presence in Texas. I ruled this out.

S. subulatum var. parviflorum (S. expansum, S. parviflorum), (23–)27–37(–42) ray florets in (1–)2 series that are usually white, sometimes pink, and dry in 1–2 outward-curling coils. Characteristics do not match the observation. Presence in Texas is southwestern. I ruled this out.

This left S. subulatum var. ligulatum (S. divaricatum), which has 17–30(–45) ray florets in one series, lavender to blue, and that dry in 3–5 coils that roll under. Present in Texas is widespread, including in San Antonio area. Description matches the observation. I selected this which, as you see, is now S. divaricatum.

Just to add that one of the most important (or two, rather) characteristics of any species in the family Asteraceae are the involucre and its phyllaries. I did not differentiate here, but there is a difference among these five. I have made a spreadsheet of the information from FNA that lists, in columnar form, the sames and differents among them. If you wish to have a copy, please message me your email address.

Posted on 08 de janeiro de 2022, 01:45 PM by elizabeth1067 elizabeth1067


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