07. Tree Identification

notes
trees
Basics techniques to identify trees.
Author

Stephen J. Mildenhall

Published

2024-10-18

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Types of Tree Leaves

Leaves are distinguished by several different characteristics, including the following.

  1. Simple vs. Compound Leaves:
    • Simple Leaves: A single, undivided leaf blade attached to the stem (e.g., oak, maple).
    • Compound Leaves: A leaf made up of multiple leaflets that are attached to a central stalk (e.g., ash, walnut).
  2. Shape:
    • Lanceolate: Long and narrow with a pointed tip, like a spear (e.g., willow).
    • Ovate: Egg-shaped, broad at the base, tapering toward the tip (e.g., birch).
    • Cordate: Heart-shaped (e.g., redbud).
    • Elliptical: Shaped like an elongated oval (e.g., beech).
    • Palmate: Shaped like an open hand with lobes radiating from a single point (e.g., maple).
  3. Size:
    • Varies greatly among species, from tiny needles (conifers) to large, broad leaves (magnolias).
  4. Venation:
    • Pinnate: A central vein with smaller veins branching off (e.g., oak).
    • Palmate: Several major veins radiating from the base of the leaf (e.g., maple).
    • Parallel: Veins run parallel from base to tip (common in monocots, like palms).
  5. Color (Top and Bottom):
    • Leaves often differ in color between the top and bottom surfaces. For example, the top may be dark green while the underside is lighter, grayish, or even white.
  6. Hairs (Top and Bottom):
    • Some leaves are hairy, especially on the underside, for protection or moisture retention. Others are smooth.
  7. Edge Type (Margin):
    • Entire: Smooth, without teeth or lobes (e.g., magnolia).
    • Serrate: Saw-toothed with sharp edges (e.g., birch).
    • Lobed: Deep or shallow indentations (e.g., maple, oak).
  8. Other Features:
    • Leaf Arrangement: Alternate, opposite, or whorled on the stem.
    • Texture: Waxy, leathery, or delicate.

Leaf Characteristics by Species

Species Leaf Type Shape Size Venation Top Color Bottom Color Hairs (Top/Bottom) Edge Type Other Characteristics
Acer platanoides Simple Palmate Medium-large Palmate Dark Green Lighter Green None/None Lobed Opposite arrangement
Betula pendula Simple Ovate Small Pinnate Bright Green Pale Green None/Hairy Serrate Triangular, alternate arrangement
Fagus sylvatica Simple Elliptical Medium Pinnate Dark Green Light Green None/None Entire Waxy, alternate arrangement
Fraxinus excelsior Compound Lanceolate Large Pinnate Dark Green Pale Green None/Hairy Serrate Opposite arrangement, 7-13 leaflets
Quercus robur Simple Lobed Medium Pinnate Glossy Green Pale Green None/Hairy Lobed Alternate arrangement
Magnolia grandiflora Simple Elliptical Very large Pinnate Glossy Green Rusty Brown Smooth/Hairy Entire Leathery texture
Ilex aquifolium Simple Ovate Small Pinnate Dark Green Pale Green None/Smooth Spiny Glossy, thick leaves, evergreen
Tilia cordata Simple Cordate Medium Pinnate Dark Green Lighter Green Smooth/Smooth Serrate Alternate arrangement, fragrant
Ulmus glabra Simple Ovate Medium Pinnate Dark Green Lighter Green Rough/Hairy Serrate Asymmetrical base
Juglans regia Compound Lanceolate Large Pinnate Bright Green Light Green Smooth/Smooth Entire Alternate arrangement, 5-9 leaflets

Types of Tree Flower

Trees exhibit a variety of flowering structures, each adapted to different pollination methods, such as wind or animal pollination. Here’s an overview of flower types in trees, including catkins and other common inflorescences. An inflorescence is a flower cluster.

  1. Catkins Catkins are long, drooping clusters of small, unisexual flowers (either male or female) found in wind-pollinated trees.
    • Male Catkins: Often release large amounts of pollen.
    • Female Catkins: Receive pollen and sometimes develop into seed-bearing structures.
    • Examples: Birch (Betula), Alder (Alnus), Oak (Quercus), Willow (Salix), Poplar (Populus).
  2. Solitary Flowers Some trees produce large, solitary flowers, often showy and designed to attract pollinators like insects or birds.
    • Magnolias (Magnolia spp.): Produce large, fragrant, white or pink flowers with spirally arranged petals. These flowers are ancient and can be pollinated by beetles.
    • Cherry (Prunus spp.): Solitary or clustered flowers with five petals, usually white or pink, attractive to bees and insects.
  3. Umbels Umbels are flat-topped or rounded inflorescences where all flower stalks arise from a common point.
    • Rowan (Sorbus aucuparia): Produces clusters of small, white flowers in umbels. These flowers are insect-pollinated and lead to the formation of red berries.
  4. Racemes Racemes are elongated, unbranched clusters of flowers with the youngest flowers at the top.
    • Black Locust (Robinia pseudoacacia): Produces drooping racemes of white or pink, fragrant flowers, pollinated by bees.
  5. Panicles Panicles are compound, branched clusters of flowers.
    • Horse Chestnut (Aesculus hippocastanum): Produces large, upright panicles of white or pink flowers, attracting bees and insects.
  6. Ament An ament is a simple, unbranched inflorescence similar to a catkin but more rigid, often in coniferous trees.
    • Hazel (Corylus avellana): Male flowers form long, pendulous aments, releasing pollen in early spring.
  7. Cyme A cyme is a branched cluster of flowers where the terminal flower blooms first.
    • Linden (Tilia spp.): Produces small, yellowish-white flowers in cymes, which are fragrant and attract bees for pollination.

Flower Types in Common Tree Species

Species Flower Type Description of Flowers Pollination Method Fruit Type (Post-Pollination)
Betula pendula Catkin Long male catkins, shorter female catkins Wind Small winged seeds (in cones)
Quercus robur Catkin Long male catkins, female flowers develop into acorns Wind Acorns
Magnolia grandiflora Solitary Flower Large, white, fragrant flowers Insect (Beetles) Aggregate drupes
Prunus avium Solitary Flower Small, white-pink, five-petaled flowers Insect (Bees) Drupe (Cherry)
Sorbus aucuparia Umbel Small, white, flat clusters of flowers Insect (Bees, Flies) Red berries
Robinia pseudoacacia Raceme Hanging clusters of white or pink flowers Insect (Bees) Legume (pod)
Aesculus hippocastanum Panicle Large, upright clusters of white or pink flowers Insect (Bees) Capsule (Horse Chestnut)
Corylus avellana Ament Long male aments, smaller female flowers Wind Nut (Hazelnut)
Tilia cordata Cyme Small, fragrant, yellowish-white flowers in cymes Insect (Bees) Nutlet (with wing for wind dispersal)
Salix alba Catkin Slender male and female catkins on separate trees Wind Capsule with fluffy seeds
Populus tremula Catkin Long, drooping male and female catkins on separate trees Wind Seeds with cottony hairs

Types of Tree Fruit

Trees produce a wide variety of fruits and seeds, which can be classified based on their structure, method of dispersal, and how they develop from the flower. Below are some common types of fruits and seeds produced by trees:

  1. Simple Fruits These develop from a single ovary of a single flower.
    • Drupes: Fleshy fruits with a single hard seed (stone or pit) inside. Examples include cherries (Prunus), plums, olives (Olea), and peaches.
    • Berries: Fleshy fruits with multiple seeds. Examples include holly (Ilex), persimmons, and avocado (Persea).
    • Pomes: Fleshy fruits with a core containing seeds. Examples include apples (Malus), pears (Pyrus), and quinces.
    • Capsules: Dry fruits that split open to release seeds. Examples include horse chestnut (Aesculus) and eucalyptus.
    • Samara: Winged fruits that help with wind dispersal. Examples include maple (Acer), ash (Fraxinus), and elm (Ulmus).
  2. Aggregate Fruits These develop from a single flower with multiple ovaries. Each ovary develops into a small fruit, but they are grouped together.
    • Aggregate Drupes: Many small drupes that form a cluster. Examples include magnolias (Magnolia) and raspberries (although raspberries are not from trees, their structure is similar to magnolia fruits).
  3. Multiple Fruits These develop from multiple flowers that fuse together.
    • Multiple Fruit: Pineapple is a classic example of a multiple fruit, but certain fig trees (Ficus) produce a multiple fruit structure known as a syconium.
  4. Dry Fruits Dry fruits either split open to release seeds (dehiscent) or remain intact (indehiscent).
    • Nuts: Hard-shelled, indehiscent fruits with a single seed inside. Examples include acorns (Quercus), chestnuts (Castanea), and walnuts (Juglans).
    • Legumes: Dry fruits that split open along two sides. Examples include black locust (Robinia) and honeylocust (Gleditsia).
    • Achenes: Small, dry, indehiscent fruits with a single seed inside. Examples include sycamore (Platanus).
    • Caryopsis: A dry fruit in which the seed is fused to the fruit wall, typical of grasses, though not common in trees.
  5. Conifer Seeds (Gymnosperms) Conifers, which are not angiosperms, produce seeds in cones rather than in true fruits. The seeds are often winged and adapted for wind dispersal.
    • Winged Seeds: Found in pine (Pinus), spruce (Picea), and fir (Abies).
    • Fleshy Arils: Some conifers, like yew (Taxus), have a fleshy, berry-like structure called an aril that surrounds the seed.
  6. Specialized Fruits and Seeds
    • Samaras: Winged fruits that aid wind dispersal (e.g., maple, ash).
    • Acorns: Hard-shelled nuts with a cap (e.g., oaks).
    • Helicopters: Some trees, like maples, produce samaras that spin when falling, helping in seed dispersal.

Fruit Types for Common Tree Species

Species Fruit Type Fruit Description Seed Dispersal Method
Acer platanoides Samara Winged fruit, pairs, often called “helicopters” Wind
Quercus robur Nut (Acorn) Hard, woody, with a cap Gravity, animals (squirrels)
Malus domestica Pome Fleshy, with a core containing seeds Gravity, animals (birds, mammals)
Fraxinus excelsior Samara Long, single-winged fruit Wind
Prunus avium Drupe Fleshy with a single hard seed (stone) Animals (birds, mammals)
Juglans regia Nut (Drupe-like) Large, hard shell encased in a green husk Gravity, animals
Fagus sylvatica Nut (Beech nut) Small, triangular nuts inside a spiky husk Gravity, animals
Magnolia grandiflora Aggregate Drupe Many small fleshy fruits in a cone-like structure Animals (birds)
Tilia cordata Nutlet Small, round, winged nutlets Wind
Ulmus glabra Samara Flat, round, winged seeds Wind
Ilex aquifolium Berry Small, bright red berries Animals (birds)

Flowering Tree Sex

All flowers can be perfect (bisexual) like cherry and apple, monoecious with both male and female flowers on one tree, like oak, hazel, and birch, or dioecious, meaning they have distinct male and female individuals, and only the female trees produce fruit or seeds. In dioecious species, the male trees produce pollen, while the female trees bear the fruit or seeds.

Genus Common Name Flower Type
Acer Maple Perfect
Alnus Alder Monoecious
Betula Birch Monoecious
Cinnamomum Cinnamon, Camphor Perfect
Corylus Hazel Monoecious
Crataegus Hawthorn Perfect
Fagus Beech Monoecious
Fraxinus Ash Dioecious
Ilex Holly Dioecious
Juglans Walnut Monoecious
Liriodendron Tulip Tree Perfect
Magnolia Magnolia Perfect
Malus Apple Perfect
Morus Mulberry Dioecious
Myristica Nutmeg Dioecious
Persea Avocado Dioecious
Populus Aspen Dioecious
Prunus Cherry Perfect
Pterocarya Wingnut Monoecious
Quercus Oak Monoecious
Robinia Locust Perfect
Rosa Rose Perfect
Sorbus Rowan Perfect
Tilia Lime, Linden Perfect
Ulmus Elm Perfect

Here are some more examples of dioecious trees where sex can be distinguished by the presence or absence of fruit or seeds:

  • Ginkgo biloba (Ginkgoopsida) Only female trees produce the characteristic smelly fruit, which contains seeds. Male trees, often preferred in urban planting, produce only pollen cones.

  • Holly (Ilex spp.) - Aquifoliales, Aquifoliaceae In dioecious species like Ilex aquifolium (common holly), only female trees produce the bright red berries. Male trees produce flowers but no fruit.

  • Willow (Salix spp.) - Malpighiales, Salicaceae Willows are typically dioecious, with male trees producing pollen and female trees producing cottony seeds. The fluffy seed tufts are only found on female trees.

  • Poplar (Populus spp.) - Malpighiales, Salicaceae Like willows, poplars are dioecious. Female trees produce catkins that develop into fluffy seeds, while male trees produce pollen.

  • Ash (Fraxinus spp.) - Lamiales, Oleaceae Ash trees can be dioecious or have a mix of male and female flowers on the same tree. In dioecious species, only female trees produce the characteristic winged seeds (samaras).

  • Boxelder (Acer negundo) - Sapindales, Sapindaceae Boxelder maples are dioecious. Female trees produce the familiar paired samaras (winged seeds), while male trees only produce pollen.

  • Juniper (Juniperus spp.) - Pinales, Cupressaceae Junipers can be dioecious, with female trees producing berry-like cones and male trees producing pollen. The cones on female junipers resemble blue berries, used to flavor gin.

  • Mulberry (Morus spp.) - Rosales, Moraceae Many mulberries are dioecious. Female trees produce the edible, berry-like fruit, while male trees produce pollen.

  • Osage Orange (Maclura pomifera) - Rosales, Moraceae Osage orange is dioecious, with female trees producing large, wrinkled fruits called “hedge apples.” Male trees do not bear fruit.

  • Date Palm (Phoenix dactylifera) - Arecales, Arecaceae Date palms are dioecious, with female trees producing the edible date fruits. Male trees are grown to provide pollen for fertilization but do not produce dates.

  • Yew (Taxus spp.) - Pinales, Taxaceae Yew trees are dioecious. Female trees produce the distinctive red, berry-like arils (fleshy seed coverings), while male trees produce pollen cones.

In these dioecious species, distinguishing between male and female trees is possible by observing the presence or absence of fruit or seed structures during the reproductive season. Male trees typically produce flowers or cones for pollen release, but only female trees bear the fruit, seeds, or cones in these species.

Identifying Common Species

General Observations

Here are some general observations on tree identification:

  • Deciduous vs. Evergreen: Trees can be classified based on whether they lose their leaves in winter (deciduous) or retain them year-round (evergreen).
  • Leaf Arrangement: Leaves can be opposite (paired directly across from each other) or alternate (staggered along the stem).
  • Leaf Type: Leaves may be simple (a single leaf blade) or compound (multiple leaflets attached to a central stem).
  • Flowering: Many trees produce flowers, which can help in identification, especially in spring.
  • Fruit and Seeds: Trees can also be identified by their fruit, nuts, or seeds.
  • Bark Texture: Bark is an excellent identifier, especially in winter when leaves are absent.

Oak (Common name: Oak)

  • Leaves: Lobed with rounded edges; alternate along the twig.
  • Bark: Deeply fissured, often with a rugged appearance.
  • Acorns: Found in clusters, sitting in shallow cups.
  • Where to Find: Ancient woodlands, parks, and hedgerows.

Ash (Fraxinus excelsior)

  • Leaves: Pinnate (feather-like), typically with 5-9 leaflets.
  • Bark: Smooth and grey when young, becoming ridged as it ages.
  • Keys: Winged seeds, often hanging in dense bunches.
  • Where to Find: Common in hedgerows and woodlands.

Beech (Fagus sylvatica)

  • Leaves: Oval, with wavy edges and fine hairs when young.
  • Bark: Smooth and grey, often with a slightly silver sheen.
  • Nuts: Small, triangular beech nuts encased in spiny husks.
  • Where to Find: Prefers well-drained soils, often in mixed woodlands.

Silver Birch (Betula pendula)

  • Leaves: Triangular, with serrated edges and a pointed tip.
  • Bark: White and peeling, with dark diamond-shaped fissures.
  • Catkins: Long, hanging catkins in spring.
  • Where to Find: Found in heathlands, open woods, and often in newly rewilded areas.

Cedar of Lebanon (Cedrus libani)

  • Needles: Evergreen needles arranged in clusters, giving a tiered, flat-branched look.
  • Bark: Dark grey to brown, often deeply furrowed.
  • Cones: Barrel-shaped and upright, taking years to mature.
  • Where to Find: Frequently seen in large estate gardens and parks, with iconic tiered branches.

Tips for Identifying Trees

  • Seasonality: Observing trees across seasons can help—pay attention to flowers in spring and fruit or seeds in autumn.
  • Leaf Arrangement: Look at how leaves are positioned on the branch. Opposite vs. alternate arrangements can be a key factor.

Next: Tree Identification pictures