Tree Twig Identification: Buds, Bundle Scars, Leaf Drops, Leaf Scars

Summary: Kim D. Coder of North America's University of Georgia in Athens, Georgia, uses buds, bundle scars, leaf drops and leaf scars for tree twig identification.

tree twig anatomy: striped maple (Acer pensylvanicum) with terminal bud breaking: Rob Routledge/Sault College/Bugwood.org, CC BY 3.0 United States, via Forestry Images

Tree twig identification appears third in four-step examinations of deciduous, evergreen and persistent-leaved trees, according to Advanced Twig Anatomy: Everyone Needs Buds (Part II) in the April 2014 issue of Arborist News.

Kim D. Coder of North America's University of Georgia in Athens, Georgia, bids master arborists, master gardeners, master naturalists and tree stewards to sequence foliage drops. Determination of twigs as deciduous from leaf drops within one calendar year or as evergreen from "persistent-leaved" foliage renewing every three years characterizes the first step. The second step demands differentiating among alternate, near-opposite, opposite or whorled leaf scars before determining the absence or the presence of false or true terminal buds.

The fourth step examines bundle scars, known as "leaf traces in newly removed leaves" or as "remnants of broken lines of vascular tissue that served" leaves.

Scars form from the "visible disruption after abscission or removal of an organ," such as when flowers, fruits, leaves, shoots and stipules fall off tree twigs. All twig scars generate information even though bud, leaf, stipule and terminal bud scars get prioritized for ecosystem stress, species-specific growth rates and tree twig identification.

Some species have "leaf-like blades, bud scale-like growths, or spine-like points" as bracts (modified leaves) whose stipular scars look "ring-like" or "slit-like" just above axillary buds.

Leaf arrangements involve one scar on alternating sides, two on near-opposite or opposite sides and three or more whorled through both sides of nodal torus rings. Their raised, surface-level or sunken positions on twigs juggle broad crescent, circular, half round, heart, horseshoe, oval, shield, thin crescent, three-lobed, triangular, U- or V-like shapes.

Completion of step two for tree twig identification sometimes kickstarts passage through steps three and four since alternate- and near-opposite-leaved species far outnumber opposite- and whorled-leaved.

Examination of tree twig buds, as "compound protective devices used to shield growing points during non-growth periods," further levels the species-specific options in tree twig anatomy. Buds may be composed of compacted or unexpanded primordial internodes, developing flower or leaf tissues, primordial lateral growing points and scaly, waxed paper-like coverings called cataphylls. Cataphylls, whose immature bracts cover growing points and growing point-related tissues, necessitate classifications as alternate-, overlapping-scaled imbricates, one-scaled singles, paired-, overlapping-scaled two-ranked or non-overlapping, paired valvates.

Scales never occur on naked buds whose growing points primordial leaves and trichomes (hairs) sometimes obscure but whose presence offers typically raised, sunken or surface-level looks.

Tree twig anatomy positions accessory buds around axillary buds, axillary buds at leaf bases, pseudoterminal buds near terminal twig scars and terminal buds at twig tips. Axillary, pseudoterminal and terminal scars qualify as indicators of axil buds near leafy twigs, the previous terminal twig shoot's death-place and the previous terminal bud's location.

All buds, sessile (stalk-less) or stalked, reveal conical to oval or round, large or small, long or short, narrow or wide and point- or round-tipped shapes. Shape also surfaces in step four, where the 12 petiole leaf-base scar shapes show cross sections of one to five-plus bundle scars or one U-shaped scar.

Tree twig identification tracks tree-related ecosystem stress, growth rates and winter identification and turns unusual facts, such as pseudoterminal bud-effected zigzag growth patterns, into backyard-friendly knowledge.

white ash (Fraxinus americana) leaf scar and terminal bud: Brett Marshall/Sault College/Bugwood.org, CC BY 3.0 United States, via Forestry Images

Acknowledgment

My special thanks to:
talented artists and photographers/concerned organizations who make their fine images available on the internet;
University of Illinois at Urbana-Champaign for superior on-campus and on-line resources.

Image credits:

striped maple (Acer pensylvanicum) with terminal bud breaking: Rob Routledge/Sault College/Bugwood.org, CC BY 3.0 United States, via Forestry Images @ http://www.forestryimages.org/browse/detail.cfm?imgnum=5472075

white ash (Fraxinus americana) leaf scar and terminal bud: Brett Marshall/Sault College/Bugwood.org, CC BY 3.0 United States, via Forestry Images @ http://www.forestryimages.org/browse/detail.cfm?imgnum=5468100

For further information:

Coder, Kim D. April 2014. "Advanced Twig Anatomy: Everyone Needs Buds (Part II)." Arborist News 23(2): 12-19.
Available @ http://viewer.epaperflip.com/Viewer.aspx?docid=1ee7afcc-6b5d-408e-aff0-a2f800b715b6#?page=26

Gilman, Ed. 2011. An Illustrated Guide to Pruning. Third Edition. Boston MA: Cengage.

Hayes, Ed. 2001. Evaluating Tree Defects. Revised, Special Edition. Rochester MN: Safe Trees.

Marriner, Derdriu. 15 February 2014. “Tree Twig Anatomy: Ecosystem Stress, Growth Rates, Winter Identification.” Earth and Space News. Saturday.
Available @ https://earth-and-space-news.blogspot.com/2014/02/tree-twig-anatomy-ecosystem-stress.html

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