26a.

Paired spines representing modified stipules present on both sides of leaf scar

27

26b.

Spines or prickles single (although sometimes very abundant), not paired on both sides of leaf scars

28

27a.

Buds hidden beneath leaf scar which often shows three irregular cracks; tree

Robinia

27b.

Buds visible, reddish, and wooly; shrub

Xanthoxylum

28a.

Woody vine; no pith differentiated in stem cross-section; stem green, with persistent petiola bases

Smilax

28b.

Erect or weak-stemmed shrubs; stem hard, gray brown, or reddish, with pith; petiole bases usually absent

29

29a.

Spines solitary at nodes, subtending buds or branches; otherwise unarmed

30

20b.

Spines in clusters at nodes or prickles scattered over stem surface

31

30a.

Twigs reddish-brown or purplish, bark firm; bud partially enclosed in base of spine; spines sometimes three-pronged but solitary

Berberis

30b

Twigs light grayish or tan with bark tending to shred; spines unbranched, sometimes in clusters of 3

Ribes

31a.

Irregular stubs of petiole present; stems elongated or arching, biennial

Rubus

31b.

Distinct leaf scars present; stems erect, capable of living more than 2 years

32

32a.

Twigs ridged or lined from nodes; bud scales loose, about 6; bark light grayish or tan and shredding

Ribes

33a.

Leaf scars, except on young fast-growing shoots, densely clustered on very short peg-like spur shoots (less than 1cm. long)

34

33b.

Leaf scars scattered along more or less elongate twigs

35

34a.

Twigs slender, with about 10-20 spurs per 10 cms.

Larix

34b.

Twigs stout with about 2-8 spurs per 10 cms.

Ginkgo

35a.

Climbing or twining vines

36

35b.

Erect trees or shrubs

37

36a.

One bundle scar; buds glabrous; twigs ridged

Celastrus

36b.

3-7 bundle scars; buds hairy

Toxicodendron

37a.

One bundle scar

38

37b.

3-several bundle scars

45