An Introduction to Winter Botany

James E. Perry, PhD, PWSDouglas A. DeBerry, PhD, PWS, PWD

February 19, 2010

Winter Botany

• Usually means “identification of woody species in winter”

• Based on careful examination of several plant characteristics which are readily identifiable in winter (particularly characteristics of the twigs)

• In most cases, winter identification is every bit as reliable as growing season ID

Key Characters

• Growth Form (Habit)• Habitat• Bark• Twigs

– Buds• Scales• Orientation

– Leaf scars• Bundle scars• Stipule scars

– Branch/fruit scars– Pith– Lenticels– Spur shoots– Armaments

Tree Sapling

Shrub Forb/Graminoid

Habit

HabitHabit

Tree Woody plants >3.0 inches DBH, regardless of height

Sapling/Shrub Woody plants >3.2 ft tall and <3.0 inches DBH

Herbaceous All nonwoody plants, and woody plants <3.2 ft tall

Woody Vine Woody climbing plants >3.2 ft tall

Habitat

• Environmental context (moisture regime)– Xeric (dry)– Mesic (moist)– Hydric (wet)

• Also important to note: aspect, slope, soil (edaphic) conditions, sunlight availability, temperature, “demographic” characteristics, geographic range

Habitat

Dry

Moist

Wet

Habitat

Quercus michauxii Nuttall

Swamp chestnut oak

http://www.biol.vt.edu/digital_atlas/

Diagnostic Characteristics

• Branching structure• Bark• Twigs• Buds• Scars (leaf, bundle, fruit/twig, stipule, scale)• Fruits

Branching Structure

• Branching structure is one of the first things to look for:

OPPOSITE-or-

ALTERNATE

For OPPOSITE branching: Only four native* tree families have opposite branching (leaf scars)

Maple (Aceraceae)

Ash (Oleaceae)

Dogwood (Cornaceae)

Buckeye (Hippocastanaceae)

[*Non-native: Princess tree (Scrophulariaceae)]

Branching Structure

Branching Structure

OPPOSITE:

Green ash(Fraxinus

pennsylvanica)

Branching Structure

ALTERNATE:

White oak(Quercus alba)

Bark

• “Periderm” = bark• Portion of woody stem lying outside of the

cambium layer; function is protection (‘skin’)• On older branches and trunks, the cork

cambium forms interior to the bark– Exterior periderm tissues die, then bark tends to

become furrowed or scaly, often with a pattern– Bark patterns can be diagnostic for species ID

Bark

Loblolly pine – “platy”“rectangular”

Green ash –“furrowed”

River birch –“scaly”

Red maple –“smooth”

Persimmon –“blocky”

Twigs• Twig – terminal portion of a branch which grew

during the current year or preceding year• Twig characteristics:

– Size (stoutness)– Color– Epicortical characters (literally ‘outside the bark’)

• Lenticels• Hairiness• Smoothness (or roughness)

– Cross-sectional shape– Pith

Twigs• Color – many species turn red during the

winter on the sun-exposed side due to pigments called anthocyanins (favored by colder weather) ex. heath family (Ericaceae)

• Epicortical features – Species like highbush blueberry (Vaccinium corymbosum) can be pubescent (hairy) with wart-like projections on the twig surface (verrucose)

Twigs

Common elderberry (Sambucus canadensis)*

* =Sambucus nigra ssp. canadensis

Epicortical features:

Lenticels – small openings in bark for gas exchange; often very prominent

Corky ridges – irregular protuberances on bark as in winged elm or sweet gum

Winged elm (Ulmus alata)

Twigs

• Pith – central portion of twig composed of parenchyma (large, thin-walled cells), usually different color than surrounding wood (xylem)– Continuous – solid and homogeneous throughout– Diaphragmed – solid with partitions (thicker-walled

cells in regularly-spaced plates); tulip tree (Liriodendron tulipifera), black gum (Nyssa sylvatica)

– Chambered – empty with partitions– Spongy – pith filled with small, irregular cavities– Excavated – pith lacking

Twigs

Note: Cross-section important for pith and twig shape

Twigs• Spur shoots – short, stubby, slow-growing

branches often crowded with leaf scars; characteristic of rose family (Rosaceae) and holly family (Aquifoliaceae)

Apple (Malus sylvestris)

Armament

Spines – sharp, modified persistent stipules (usually paired)

Prickles – outgrowths from young bark; usually scattered over the surface

Thorns – sharp-pointed, modified branches

Prickles

Thorns

Spines

Twigs

Buds

• Bud – a “growing point”; early, undeveloped stage of a leafy shoot or flower

• Bud scales – reduced, modified leaves covering and protecting the embryonic growth within the bud– Imbricate – overlapping scales– Valvate – usually two, non-overlapping (“praying”)– Naked – bud scales lacking

Buds

Types of bud scales

Buds• Orientation of buds

– Terminal – bud occurs at tip of branch– Lateral – bud occurs along side of branch

• Axillary – bud occurs in the angle between the petiole of the leaf and the branch (axil)

• Accessory – buds adjacent to the main (axillary) bud– Collateral – accessory buds to the right or left– Superposed – accessory buds above the main (axillary) bud

– Pseudoterminal – when a true terminal bud is not formed and stem growth continues until cold causes young shoot to die back; shoot is ‘self-pruned’ at the highest lateral bud formed, which appears to be a terminal bud but is really not

Buds

Oaks (Quercus spp.) have one terminal and four lateral buds, giving the appearance of five terminal buds.

Buds: Special Cases

American beech (Fagus grandiflora) has alternate

sharp terminal buds

Members of Elm Family (Celtus, Ulmus) have pseudoterminal buds that give them a zig-zag shape

Buds: Special Cases

True poplars (Populus spp.) have buds that are large and sticky to the touch

Pseudo-terminal

Beech andOak

Naked

Scars• Leaf scar – distinct area left on branch after leaf has fallen;

covered by corky abscission layer, laid down at the point of attachment of the petiole, which seals the living tissues beneath – Leaf scars can be highly variable in shape, size, and arrangement

Scars• Bundle scar – point where vascular tissue passed from stem to leaf,

visible within the leaf scar (also called a “bundle trace”)• Stipule scar – stipules are small, leaf-like appendages attached at the

base of the leaf petiole on many trees, often leaving behind a linear scar after abscission

Scars

• Branch scar – in cases where species do not form terminal buds, withered tip of shoot often sloughs off leaving circular scar behind

• Fruit scar – very similar in appearance to branch scars, represent the abscission point between the stem and fruit-bearing appendages

Scars: Special Cases• Members of magnolia family

(Magnoliaceae) and American sycamore (Platanus occidentalis)have stipule scars that surround the twigs

Fruits

• Fruit – ripened ovary with one or more ripened ovules, also known as seeds

• Pericarp – the fruit wall developed from the ovary wall; can be fleshy or dry, or somewhere between

Fruits

• Fleshy fruits:– Drupe – “stone” fruits, like peach (also black

haw, hackberry, holly)– Pome – apple-like fruits (apple, hawthorn,

chokeberry)– Rose hip – fleshy aggregate fruit

Fruits

• Dry fruits that are “dehiscent” (split open):– Legume – “pod” like fruits splitting down two

sides (sutures) (redbud)– Follicle – similar to legume but only splitting

down one side (ninebark)– Capsule – two or more carpels (compartments)

(catalpa, princess tree)

Fruits

• Dry fruits that are “indehiscent” (do not split open, but rather fall intact):– Achene – small fruit with pericarp closely enveloping

the seed (sycamore)– Samara – like an achene but with a wing to assist in

wind dispersal (ash, maple “helicopters”)– Nut – also similar to an achene, but with a hard,

leathery or bony pericarp (chestnut, beech)– Acorn – specialized oak fruit with nut borne in a cap-

like structure

Gymnosperm “Fruits”

• The seeds of conifers and cone-bearing species are not enclosed in a pericarp, but borne exposed on cone scales (Gymnosperm = “naked seed”)

• Cone – arrangement of seed-bearing scales about a central axis

Data Sources on the WebData Sources on the Web

• USDA Plants Database http://plants.usda.gov/plants/

• VT Forestry site: http://www.cnr.vt.edu/dendro/dendrology/factsheets.cfm

• Virginia Atlas: http://www.biol.vt.edu/digital_atlas/

Other Data SourcesOther Data Sources

Key to Winter Twigs(http://www2.una.edu/pdavis/Twig%20Key.htm)

In part, after Preston & Wright's Identification of Southeastern Trees in Winter N.C. Agri. Exten. S. AG-42