| Upper surface | B. swaseyi | B. trifoliolata | hybrids |
|---|---|---|---|
| Harms (Central Texas) | dull, grayish green, uncommonly glaucescent, clearly reticulate | lustrous, yellow-green to blue-green, ±glaucous, venation weak to prominent | lustrous, dark green to blue–green, uncommonly glaucescent, clearly reticulate |
| Ahrendt 1961 | grey-green fairly closely reticulate | slightly lustrous green, epapillose, subenervate | ––– |
| Whittemore (FNA v. 3) | dull, somewhat glaucous | dull, ±glaucous | ––– |
| Correll & Johnston 1970 | grayish green or yellowish-green | greyish-green and sometimes glaucous | ––– |
| Vines 1960 | ––– | pale green, glabrous reticulate white-veined | ––– |
On our study plot B. trifoliolata adaxial leaf surfaces are generally somewhat lustrous and vary considerably in color — from yellowish–green to bluish–green, and from non–glaucous to mostly glaucous. Primary and secondary veins are generally conspicuous, the central vein always wider and paler than adjacent surfaces. The visibility of lesser veins varies a great deal, but the strongly reticulate pattern of the abaxial surface is never apparent. A somewhat greater degree of variability was found in Bexar County (Government Canyon State Natural Area) some 90 miles south, with a large number of bushes that had a deep blue–green cast (bottom central above). In other areas of Central Texas, from Enchanted Rock (Burnet County) to Travis County I noted very little, if any, variation in leaf surface — with non-glaucous forms in the east and more glaucous forms in the west.
Some differences in the above descriptions may well reflect the wide variation by individual plant and locale.
Mature B. swaseyi leaflets are dull, subdued green, visibly reticulate and sometimes glaucescent. Unlike B. trifoliolata, the upper leaf surface of B. swaseyi plants varies little in color and venation - unless one also considers different stages of leaf development for a single bush. For example, young spring leaves are light yellowish-green, but quickly lose the yellowish cast and darken with maturity. Leaves that emerge after summer rains tend to be reddish. The leaves of most plants acquire a maroon cast or even turn maroon entirely with fall/winter frosts.
Although hybrid leaves exhibit a wide range of surface qualities, in general they seem to share the lustre of B. trifoliolata and the visible reticulate venation of B. swaseyi. In color they are overall somewhat darker, often more toward blue–green than B. trifoliolata, with minimal or no glaucescence. From a distance they often appear to be B. trifoliolata. Fresh spring leaves are like those of B. swaseyi, but mature deeper green leaves persist throughout the year, lacking the winter maroon shift. At one point I used the absence of the winter maroon shift as an indicator of hybridization, but some apparent B. swaseyi bushes do not exhibit this color change.
| Lower surface | BESW | BETR | hybrid |
|---|---|---|---|
| Harms (Central Texas) | paler than adaxial surface clearly reticulate papillose | paler than adaxial surface prominently reticulate not papillose | paler than adaxial surface clearly reticulate ±papillose |
| Ahrendt 1961 | pruinose grey fairly closely reticulate | subenervate | ––– |
| Whittemore (FNA v. 3) | dull, papillose | dull, papillose | ––– |
| Correll & Johnston 1970 | paler conspicuously venose | ––– | ––– | Vines 1960 | paler, reticulate-veiny | paler less prominently reticulate | ––– |
The dominant feature of B. trifoliolata's lower leaflet surface in Central Texas is its prominent reticulate venation, with only the primary vein raised. The color is always paler with a less blue cast than the corresponding upper surface. It is neither papillose nor glaucous. However, in West Texas, as is apparent from the above images, it is strongly papillose and with raised primary and secondary veins, but lesser reticulate venation is not visible. (For discussion and images of papillose B. trifoliolata var. glauca.)
Lower leaflet surface of B swaseyi is clearly reticulate with raised secondary veins. It is papillose, clear under stronger magnification, which gives the already paler green surface a gray cast.
Hybrid leaflets exhibit none to minimal papillosity, requiring much higher magnification to be seen, with surface color intermediate between the two clear species as well. They are clearly reticulate, with secondary veins generally not raised.
| no. of plants |
Apparent at | concentration at veins |
comment | ||
|---|---|---|---|---|---|
| 10X | 40X | ||||
| B. swaseyi | 8 | 7 | 1 | 4 | 1 was barely visible at 10X | putative hybrids | 11 | 4 | 4 | 2 | 2 were uncertain at 40X 1 lacked papillae |
B. trifoliolata | 20 | 0 | 0 | ––– | No potentially papillose plants were found. |
B. swaseyi has a minutely papillose under-surface, often not apparent without a good light source and high magnification. With some plants the papillae appear to be concentrated along the main veins. B. trifoliolata's green coloration and minutely bullate surface sharply contrast with B. swaseyi's under-surface. No B. trifoliolata plants I have examined in our Central Texas area support Whittemore's description of "abaxially dull, papillose" (which he applies to both species).
B. trifoliolata with papillose surfaces (cf. B. trifoliolata var glauca) is unknown in our area, although both glaucous and nonglaucous foliage is common.