Distinctive Leaf Structure

Distinctive Characteristics of Our Berberis in the Current Literature

by Bob Harms email-here


B. trifoliolata	Hybrid (H12) & B. swaseyi (S22)

Number of Leaflets

The current literature might seem to indicate that for Central Texas, counting leaflet pairs suffices to distinguish our two species.

	Leaflet number		B. swaseyi with
	B. trifoliolata	B. swaseyi	stalked terminal leaflet	reduced basal leaflet pair
Ahrendt	3	5 – 7	—	yes
Whittemore	3	5 – 9**	mostly*	yes?***
Correll & Johnston	3	5+	yes*	—
	* Both specify a sessile terminal leaflet as a distinctive key feature of B. trifoliolata. The key indicates a total range of (3 –) 5 – 11 for B. swaseyi and 3 other species. * All Whittemore says is: "basal pair of leaflets sometimes reduced to bristles" (see my comment below)

The sessile/stalked terminal leaflet as a distinctive feature

All agree that the terminal leaflet of B. trifoliolata is sessile — and this is a key feature for both Whittemore and Correll & Johnston. But Whittemore's key seems to contrast 'sessile' for B. trifoliolata with 'stalked' for B. swaseyi (and 3 other species):

Leaves 5-11-foliolate (sometimes a minority of leaves 3-foliolate); terminal leaflet stalked on most or all leaves.

Thus at least some leaves may have unstalked (?sessile) terminals. But sessile and stalked are not binary opposites. All B. swaseyi terminal leaflets, stalked and unstalked, are actually sessile on the terminal rachis node (abscission joint), which is generally separated along the rachis from the topmost leaflet pair (thus, the 'stalk'). For hybrids the topmost leaflet pair and the terminal leaflet generally share the topmost rachis node, even if that terminal leaflet is not strictly sessile.

B. swaseyi terminal leaflet nodes, abscission zone enlarged at right.

For image details of the sessile/stalked terminal leaflets.

B. swaseyi's reduced basal leaflet pair

Ahrendt describes the reduced leaflet pair of B. swaseyi as:

"...the lowest pair shorter and broader... set only 1-2 mm. above the base of the rachis"

Whittemore also notes reduction of the basal leaflet:

"...basal pair of leaflets sometimes reduced to bristles"

Although I'm not certain what a bristle might be, a wide range of reduction from simply smaller to no more than a central vein tipped with a spine but with no lamina was noted. Somewhat more bristle-like are the stipules at the base of the petiole. But a greatly reduced leaflet, unlike elongated stipule teeth, is always attached at a rachis articulation ring (cf. discussion of leaf disarticulation).

normal small	2-spined	fully reduced	stipule

B. swaseyi basal leaflet size & reduction (plus stipule) For page with larger images of basal leaflet reduction.