an introduction to winter botany
TRANSCRIPT
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