A Generality Worth Notice (on the Differences in Gestalt Between Species and Genera)
There is often as much difference in branching habit, bark, and overall gestalt (of leafless tree at least) between different species of a genus as between different genera.
This hit me more than usual in Soquel today, first by seeing a big Juglans nigra next to a big J. regia on S. Main Street, then, at Sadie’s place, the difference between Quercus dentata and Q. macrocarpa, but even more so between Castanea dentata (with smooth, gray bark and slender twigs—already leafing out!!) and C. sativa with its rough? Brown bark and thick, heavy, brown twigs.
And then there are the various cultivated species of Prunus, no two alike in leaf, flower, branching, gestalt, even habitat.
- P. avium—with sparse but thick, more-or-less virgate branches and stubby flower spurs.
- P. cerasifera—with extreme, dense, intricate, slender/spinose branching.
- P. armeniaca, P. amygdalus, etc. etc., not to mention.
- P. ‘j?’—and the other flowering cherries with filmy, horizontal branching
- P. mume—with green twigs and fat, single flowers
- P. persica—with long, slender, short-lived branches
- P. cerasus, P. domestica and insititia and spinosa—
- P. salicifolius and hybrids—
- P. tomentosa and other shrubby species—
Even within a single species there can be great variation.
Quercus agrifolia—extreme variations in bark (e.g. at Arboretum entrance) and also acorns
- virginiana—extreme variation in leaves and especially growth habit but not in acorns
Pines have endless variations on a quite single theme:
- Bark of all kinds
- Needles long or short, thick or thin, blue-green to yellow-green, 1 to 5 in a cluster
- Cones and seeds of all sizes
- Growth habit from short and round to tall spires to umbrella shape
- Habitats from maritime to treeline, marsh to desert, hot to cold
Aesculus from A. californica to A. hippocast.
Genera with less variability between species (in habit and gestalt)
- Salix more or less
- Populus more or less
- Acer more or less
- Abies
- Picea
- Larix
The practical implications of all this (for gardening), apart from habitat differences etc., i.e. basically aesthetic considerations, is that some genera (Acer, Salix, etc.) can be grown as collections, i.e. many species together, and still make a harmonious overall effect, whereas other genera (Juglans, Prunus, etc.) can’t.