Archivos de diario de marzo 2018

16 de marzo de 2018

Three Similar Toadshades in SE USA

Trillium decipiens, T. reliquum , and T. underwoodii form a group of three closely related species. Here are my notes for distinguishing them from one another, taken from the monograph where the other two were first segregated from a broader concept of T. underwoodii.

T. decipiens T. underwoodii T. reliquum
stalk (scape)
erect erect decumbent*
stalk : leaf
length ratio
2.5 - 3.0
leaf tips don't touch ground
1.0 - 2.5
leaf tips often touch ground
1.6 - 2.0
leaf surfaces at or near ground level
carriage at flowering
divergent-spreading horizontal,
or curving back down to touch leaves
length : width ratio 3.0 - 3.5 3.5 - 4.0 3.5 - 4.0
broadly oblanceolate - obovate narrowly oblanceolate to narrowly elliptic usually narrowly elliptic,
but variable
length : width ratio 2 - 3 3.5 - 5 3.5 - 4
occasionally broader
color highly variable, from
green to yellow-purple to brown-purple
(rarely yellowish)
(rarely yellowish)
anther sac dehiscence lateral lateral introrse
stamen : carpel
height ratio
≈ 1.5 ≈ 1.5 ≥ 2
leaf shape lanceolate
(straight line from widest point to apex)
(straight line from widest point to apex)
broadly elliptic
(convex curve from widest point to apex)

*not nearly as decumbent as Trillium decumbens. In the T. reliquum population I visited, the stalk (scape) will sometimes only hint at 'laxness' with a slight 'S' bend, but at least some plants in a given population should have scapes that grow initially along the ground.

Publicado el 16 de marzo de 2018 23:25 por ddennism ddennism | 2 observaciones | 0 comentarios | Deja un comentario

28 de marzo de 2018

Two Blue Cohosh Species

Caulophyllum thalictroides and Caulophyllum giganteum are separate species according, as far as I can tell, mostly to this paper. However, it occurs to me, reading this paper, that physiological effects of early emergence could confound the determination of the morphological details used in this study.

For example, if the emergence and flowering phenology of C. giganteum is earlier, and if the vegetative characters that supposedly distinguish the species continue to expand and grow, as do many forest herbs, then the vegetative characters could appear larger for supposed C. giganteum plants just as a consequence of their head-start. This could be a problem as long as all the plants in this part of the study were sampled on the same day-of-the-year, rather than day-since-emergence (they were).

"On the collection date of the mass sample, 11 May 1982, C. giganteum had completed flowering while C. thalictroides was in anthesis." But how were such plants assigned species-identifications, then? Hopefully not by the same morphological characters that were used in the PCA!

The vegetative morphological characters in the single-population experiment:

Vegetative differences in C. giganteum (all longer and/or bigger):

  1. leaflet length and width of the first two leaves
  2. leaflet sinus length of the first two leaves
  3. primary petiolule length of the first two leaves
  4. terminal inflorescence length
  5. and a decrease in the degree of compounding of the second leaf.

The authors also show that flower size differences distinguish the species. (This part is from herbarium specimens across the ranges of all three species in the genus.)

  1. stamen length
  2. sepal length
  3. pistil length
  4. petal length
  5. ratio of filament length to anther length
    (but you shouldn't use ratios in this type of analysis)

In this case, they found convincing evidence of a bimodal distribution along PCA1 (composed of the above 5 characters, in decreasing order of importance, and with the same positive valence), which suggests two morphologically distinct species, one big-flowered and one small-flowered. However, this shows no evidence of the claimed phenological separation, and doesn't really show evidence of other traits that supposedly differentiate the species (flower number per inflorescence, perianth color). Herbarium specimens are not always the most representative examples of a given population, and there may well have been plants in the C. giganteum populations that had smaller flowers that were less conspicuous to the collectors.

A common greenhouse experiment might be necessary to determine whether there really is separation here, and I'd like to see evidence that organ expansion has completed by the time of its determination in the first part of this study. But maybe first I should observe some of these populations for myself:

The closest Caulophyllum locations to me:

For my late April trip to Shenandoah:

on the way down:

in and around Shenandoah:

Publicado el 28 de marzo de 2018 19:43 por ddennism ddennism | 4 comentarios | Deja un comentario