E. sericeus Calcium Oxalate Crystals [Hays Co.],
(Transmitted light scan)

by Bob Harms ()

I think it is safe to say that the conspicuous dots in the above transmitted light scan of an E. sericeus leaf are Calcium oxalate crystals. Both a leaf-clearing and free-hand cross-sections of leaves from the same population revealed druse crystals.

400x & 40x, of Druse crystals in an E. sericeus leaf cleared and stained for venation — most tissue was digested with NaOH,
but not the veins (magenta) and crystals. The crystals light up with a polarizing filter.
[Click to enlarge]

Transmitted light scans of narrow–leaf E. discolor from Jeff Davis Co. in the Trans-Pecos also show conspicuous dots (image below), but cleared leaves of that area did not show crystals. Note also that these dots are more elongated. Free-hand cross-sections suggest that they might be inter-cellular air spaces.

Since the Hays Co. specimen is from a calcareous hill country area, we can't rule out the possibility that its context accounts for why it alone developed crystals. On the other hand, E. nuttallianus leaves from the very same Hays Co. ranch did not have crystals. None of the cleared E. nuttallianus leaves showed crystals.

E. discolor immature tip leaf, Jeff Davis Co. (Trans-Pecos)	E. discolor matching 'dots' on upper/lower leaf surfaces, Jeff Davis Co.

Leaves from 30 Evolvulus collections were cleared using NaOH in order to study venation patterns, and, as a fringe benefit, this process did not dissolve Calcium oxalate crystals. Inspection of the 30 leaves found crystals in only 3 collections — E. sericeus from Hays Co. and Kleberg Co. plus E. alsinoides from Cameron Co., these latter two from South Texas. The E. alsinoides leaf, unlike the others, showed crystals only along the veins. [The crystals do not show at 45x with a dissecting microscope; a compound microscope is required.]

E. nuttallianus [click for larger leaf portion]

Missouri	Hays Co.	Bell Co.	Dallas Co.	Winkler Co.

E. alsinoides [click for larger leaf portion]

Willacy Co.	Hidalgo Co.	Cameron Co. Leaf from this collection had crystals.	Val Verde Co.	Presidio Co.
— — — Far South Texas — — —			West Edward's Plateau	Trans-Pecos

Additional E. sericeus & E. discolor images [click for larger leaf portion]

E. sericeus, Brazos Co.	E. sericeus, Nueces Co.	E. discolor, Jeff Davis Co.	E. discolor, Chihuahua	E. discolor, Coahuila
— — — E. & S. Texas — — —		— — — Trans-Pecos & Mexico — — —