Winter Botany

I.  Bud Features (Figure 1)

A.  Type of bud.  Either floral or vegetative 

B.  Bud scales.  Most buds covered w/ scales, but some are naked or embedded.

C.  Bud position.
1.  Axillary (= lateral)
2.  Terminal
3.  Pseudoterminal.  Dead branch tip may persist or fall off leaving a branch scar  (e.g. Tilia) - not to be confused with the leaf scar.  Does not show bundle scars but concentric rings (bark, wood, pith).

D.  Arrangement.  Since buds usually occur above leaf scars, shows same arrangement as leaves, i.e. alternate, opposite, and whorled.

E.  Accessory buds.  When more than one bud occurs at a node. 
1.  on either side of normal lateral bud = colateral bud (e.g. Lindera).
2.  inserted above lateral bud = superposed (e.g. Juglans)

F.  Bud scale arrangement
1.  Valvate - scales meet at their margins (e.g. Cornus, Liriodendron).
2.  Imbricate - scales overlap (e.g. Acer, Quercus, many others)

II.  Leaf Scars & Stipule Scars (Figure 2)

A. Origin. Formed in deciduous woody plants when the petiole breaks from the stem at the abscission zone.

B. Shapes.  Horseshoe, crescent, round, 3-lobed, etc.

C.  Bundle scars.  Scars indicate where the veins entered the petiole.  Their shape, number and arrangement is informative.

D.  Stipule Scars.  If present, on stem near leaf scar (e.g. Platanus, Betula)

III.  Bud Scale Scars. 

A.  Origin. Left by scales of terminal bud of previous season (hence farther down on twig, some distance from current terminal bud).

B.  Can be used to determine age of twig (until covered w/ bark).

IV. Pith
A.  As seen in longitudinal section (l.s.) of twig:
1.  Homogeneous
2.  Spongy
3.  Diaphragmed (solid with partitions)
4.  Chambered (hollow with partitions)
B.  As seen in cross section (x.s.) of twig:
1.  round
2.  3-angled
3.  5-angled, etc.

V. Other Features

A.  Lenticels.  Shape, arrangement, etc. important (e.g. Prunus).

B.  Spines and Thorns.

C.  Spur shoots.  Plant may have "normal" and spur shoots on same plant.  Spur shoots grow slowly resulting in a short, stocky, compressed branch (e.g. Pyrus, Prunus, Ginkgo).

D.  Bark.  Trunk bark and twig bark important.  Twigs can have green (photosynthetic) bark, wings (e.g. Ulmus alata, Liquidambar), or other important features.

E.  Leaves.  Some species are deciduous but the leaves (or parts of them) persist for some time on the plant.(e.g. some oaks).

F.  Fruits.  Very helpful for indentifying trees!

Twig Photographs - plants you will see in laboratory

SIUC / College of Science / Elements of Plant Systematics
URL: http://www.plantbiology.siu.edu/PLB304/WinterBotany/WinterBotany.html
Last updated: 26-Jan-08 / dln