October 08, 2020

Solanum - Morelloid clade in and around Fort Bend County, TX -- Very confusing!

The Solanum Morelloid clade (I think also referred to by some as the S. nigrum complex) is very confusing.

I realized some years ago that this group has been undergoing a lot of scrutiny by the scientific community (phylogenists/taxonomists) and that I could not rely on the keys found in Correll & Johnson's "Vascular Plants of Texas" as the species nomenclature was definitely changing. And, unfortunately, FNA has not yet published its information on the Solanaceae.
From previous research online I was already aware that there was some confusion in regards to a species known as S. ptychanthum. Apparently while S. ptychanthum was shown on range maps as occurring in this area (around Fort Bend county, TX) and S. americanum being shown as expected in more northerly parts of the US, there was information available claiming that S. americanum would, in fact, be the proper designation for what we had been calling S. ptychanthum in our area and that what some had been calling S. americanum in more northern areas is in fact to be called S. ptychanthum.

Two traits used to differentiate the two species were:
1.)Young green berries of S. americanum having specks of white (fruits turning shiny black with age), while those of S. ptychanthum are not flecked with white.
2.) Undersides of young leaves and shoots being tinged with purple in S. ptychanthum, but not in S. am.
(Unsure if this trait is particularly reliable?)

All my photos (from pre iNat days) that I had thought were S. ptychanthum turned out to fit the descriptions being given for S. americanum (white flecked young fruits, no purple tinging of leaves).

A recent observation posted by mhebert (https://www.inaturalist.org/observations/61673100) in which the suggested identification was S. emulans sent me searching the web once again for information as I had not heard of this species. I assumed that this observed plant should be S. americanum. However......

In my web search I found a paper by Sandra Knapp, Gloria E. Barboza, Lynn Bohs, Tiina Särkinen (see https://phytokeys.pensoft.net/article/31738/element/7/0/solanum%20emulans/) entitled 'A Revision of the Morelloid Clade of Solanum L. (Solanaceae) in North and Central America and the Caribbean'.
It turns out that Lynn Bohs (University of Utah) is listed on FNA's Future Volumes site as the person responsible for the genus Solanum -- This would suggest that this paper (published May 2019) might give some insight into what FNA will eventually publish in regards to these Solanum species within this clade/complex.

From what I was able to glean from the above mentioned paper's range map information, there are three species which definitely are possibilities in the area in and around Fort Bend County, TX:

S. americanum. S. emulans, and S. nigrescens. (Note that the paper considers S. emulans to be the proper name for S. ptychanthum).
In Texas:
S. americanum is shown to occur in the se 1/3 of the state (as well as long the Gulf Coast to FL & up the Atlantic coast to the Carolinas). BONAP shows a similar range. USDA shows S. a. as occurring from FL - LA, but not the TX coastal plain. [I believe these range maps have been modified at some time as I cannot recall this being the quite the distribution I remember from my previous research, but I may be misremembering.]
S. emulans is shown to occur extensively in the eastern 1/2 of the US and the southern edge of the range in TX to be what looks to be just north of Fort Bend county.
S. emulans is not a species included on either BONAP or USDA.

Both sites, however, do include a map for S. ptychanthum -- BONAP's map generated in 2014
(and posted as of today 10-8-20) shows it occurring in the eastern 2/3s of the US and in Texas south
of a line from DFW to Jeff Davis county. USDA shows a similar range (extending somewhat further
west in some states).
S. nigrescens is shown to occur roughly south of a line from the Florida panhandle west through the coastal plains to LA and on into TX out towards the Big Bend region. BONAP indicates S. nigrescens as a native species occurring only in southern AZ, while USDA shows it as a non-native occurring in coastal AL, Florida, and along the Atlantic coast from GA to NC. (Lots of discrepancies here).
One other species, S. douglassii, is shown in the above mentioned paper to inhabit parts of far West TX & through the NM&AZ into CA. BONAP and USDA both indicate this plant as occurring further east in TX and into LA (so another discrepancy).
{NOTE: only S. americanum is discussed in Correll & Johnson's "Vascular Plants of Texas".}

The paper by Knapp, Bohs, and cohorts provides a key and in depth descriptions of these 4 species as well as others in the clade occurring in other parts of the US.
To differentiate these species fully requires not only investigating some traits easily visible in photos (especially when the plants are in fruit), but also measurements of certain features (e.g. anther length, corolla sizes, calyx measurements) that are not immediately ascertainable from most photographs.

This group of plants seems like the perfect opportunity for those of us in the iNaturalist community to help the scientists by posting more precise information on these plants.

I plan to reread and digest this paper to come up with a list of traits that should be more closely scrutinized, so that observation postings can be made more informative. I will endeavor that add to this post or make another journal posting of my thoughts on this subject.

Any insights from others would be much appreciated.

Posted on October 08, 2020 22:03 by sbdplantgal sbdplantgal | 2 comments | Leave a comment