Achene: small, dry and hard one-seeded fruit.

Acorn: nut-like fruit of an oak with a scaly or warty cap.

Alternate leaves: leaves arranged on alternating sides of the twig.

Angiosperm: class of plants that has the seeds enclosed in an ovary; includes flowering plants.

Annual rings: a layer of wood – including spring-wood and summer-wood – grown in a single season; best seen in the cross-section of the trunk.

Awl-like leaves: short leaves that taper evenly to a point; found on junipers and redcedars.

Berry: fleshy fruit with several seeds.

Bisexual flower: a perfect flower; a flower with organs of both sexes present.

Broadleaf: trees having broad, flat-bladed leaves rather than needles; also a common name for hardwoods.

Cambium: layer of tissue one to several cells thick found between the bark and the wood; divides to form new wood and bark.

Capsule: dry fruit that splits open, usually along several lines, to reveal many seeds inside.

Chambered pith: pith divided into many empty horizontal chambers by cross partitions.

Common name: familiar name for a tree; can be very misleading because common names vary according to local custom, and there may be many common names for one species.

Compound leaves: leaves with more than one leaflet attached to a stalk called a rachis.

Conifer: trees and shrubs that usually bear their seeds in cones and are mostly evergreen; includes pines, firs spruces, yews and Douglas Fir.

Cross-section: surface or section of tree shown when wood is cross-cut; shows the circular growth rings.

Deciduous leaves: leaves that die and fall off trees after one growing season.

Dichotomous key: a key to tree identification based on a series of decisions, each involving a choice between two alternate identification characteristics.

Diffuse-porous: a type of hardwood in which vessels in the spring-wood are the same size as vessels in summer-wood (maples, birches, poplars, etc.).

Dioecious: having unisexual flowers with staminate (male) and pistillate (female) flowers borne on different trees.

Drupe: fleshy fruit with a single stone or pit.

Elliptic: resembling an ellipse and about one-half as wide as long.

Entire margin: leave margins that are smooth (not toothed).

Evergreen: trees and shrubs that retain their live, green leaves during the winter and for two or more growing seasons.

Family: group of closely related species and genera; scientific name ends in "aceae".

Forest ecology: study of the occurrence of forest plants and animals in respect to their environment.

Genus: a group of species that are similar; the plural of genus is genera.

Glabrous: Smooth, with no hair or scales.

Gymnosperm: large class of plants having seeds without an ovary, usually on scales of a cone; includes conifers and the ginkgo.

Hardwoods: usually refers to trees that have broad-leaves and wood made up of vessels; similar to angiosperms.

Heartwood: nonliving wood (often dark) found in the middle of a tree's stem.

Imperfect flower: a unisexual flower with either functional stamens or pistils but not both.

Inflorescence: the flowering portion of a plant.

Lanceolate: lance-shaped; about 4 times as long as wide and widest below the middle.

Lateral buds: buds found along the length of the twig (not at the tip); they occur where the previous year's leaves were attached.

Leaflets: small blades of a compound leaf attached to a stalk (rachis); without buds where they attach.

Legume: fruit that is a dry, elongated pod that splits in two, with seeds attached along one edge inside.

Lobed margin: leaf margin with gaps that extend more or less to the center of the leaf.

Lustrous: glossy, shiny.

Monoecious: having unisexual flowers with staminate (male) and pistillate (female) flowers borne on the same tree, though often on different branches.

Multiple fruit: fruit made up of a cluster of ripened ovaries that came from many separate flowers attached to a common receptacle.

Naturalized: nonnative trees that have escaped cultivation and are growing in the wild.

Needle-like leaves: very thin, sharp, pointed, pin-like leaves; found on pines, firs and some other softwoods.

Node: the point on a stem at which leaves and buds are attached.

Nut: hard, dry fruit with an outer husk that sometimes does not split open readily and an inner shell that is papery to woody.

Obovate: inversely ovate.

Opposite leaves: leaves arranged directly across from each other on the twig.

Orbicular: circular in outline.

Oval: broadly elliptic, with the width greater than one-half the length.

Ovate: having the lengthwise outline of an egg, widest below the middle.

Palmately compound: compound leaves in which several leaflets radiate from the end of a stalk (rachis); like the fingers around the palm of a hand.

Perfect flower: a bisexual flower with functional stamens and pistils.

Persistent leaves: leaves that remain on the tree during winter.

Petiole: a slender stalk that supports a simple leaf.

Phloem: inner bark of a tree that carries food and sugars from the leaves to other parts of the tree.

Photosynthesis: process through which the leaves, with energy from sunlight, make food from water and carbon dioxide.

Pinnately compound: compound leaves in which leaflets are attached laterally along the rachis or stalk; leaves may be once, twice, or three-times pinnately compound.

Pistil: the ovary-bearing (female) organ of a flower.

Pistillate flower: a unisexual (female) flower bearing only pistils.

Pith: soft and spongy, or chambered tissue found in the middle of the stem.

Polygamo-dioecious: having unisexual flowers with staminate (male) and pistillate (female) flowers borne on different trees, but also having some perfect flowers on each tree.

Polygamo-monoecious: having unisexual flowers with staminate (male) and pistillate (female) flowers borne on the same tree, along with some perfect flowers on each tree.

Polygamous: Having some unisexual flowers and some bisexual flowers on each plant (can be polygamo-monoecious or polygamo-dioecious).

Pome: fruit with a fleshy outer coat and a stony layer (similar to plastic) within, with seeds inside the stony layer (apples, pears, etc.).

Pubescent: covered with hairs.

Rachis: the central stalk to which leaflets of a compound leaf are attached.

Radial-section: surface or section of a tree shown when wood is cut down its length straight through the middle.

Rays: ribbon-like groups of vessels, tracheids and fibers that move water and other substances in the xylem between inner and outer rings and the phloem; best seen in radial sections of the trunk.

Rhombic: with an outline resembling a rhombus (diamond-shaped).

Ring-porous: type of hardwood in which the vessels in spring-wood are much larger than vessels in summer-wood (oaks, ashes, elms etc.).

Samara: dry fruit with one or two flat wings attached to a seed (as on elms and maples).

Sapwood: living wood, often light colored, found between the bark or cambium and the heartwood, usually darker colored.

Scale-like leaves: small, short, fish-scale-like leaves which cover the entire twig; found on juniper and redcedar.

Scientific names: Latin-based names used world-wide to standardize names of trees and other plants and animals.

Semi-ring-porous: type of hardwood in which the vessels in the spring-wood are somewhat larger than vessels in summer-wood; between diffuse-porous and ring-porous (black cherry, black walnut, etc.).

Serrate: with teeth.

Shade intolerant: trees that need a lot of sunlight for growth and survival.

Shade tolerant: trees that can tolerate less sunlight for growth and survival.

Shrub: low-growing woody plant with many stems rather than one trunk.

Simple leaves: leaves with one blade attached to a petiole, or stalk.

Sinus: a recess between two lobes.

Softwoods: usually refers to trees that are conifers or cone-bearing; conifers generally have softer wood than angiosperms or hardwoods, but there are many exceptions.

Solid pith: pith that is not divided into chambers.

Species: trees with similar characteristics and that are closely related to each other; species is used in both the singular and plural sense (specie is not proper).

Spring-wood: wood on the inside of an annual ring, formed during the spring; cells are often thinner-walled.

Stamen: the pollen-bearing (male) organ of a flower.

Staminate flower: a unisexual (male) flower bearing only stamens.

Strobile: a cone or inflorescence with overlapping bracts or scales.

Summer-wood: wood on the outside of an annual ring, formed during the summer; this wood is sometimes dark and cells are often thicker-walled.

Tangential-section: surface or section of a tree shown by cutting a tree lengthwise, but not through the middle.

Terminal buds: bud appearing at the apex, or end, of a twig; usually larger than other lateral buds.

Toothed/serrated margin: leaf margin with coarse, fine, sharp or blunt teeth.

Tracheids: small-diameter tubes in the wood of trees that carry water from the roots to the leaves; water carrying tubes in conifer xylem are all tracheids.

Tree: a woody plant with one to a few main stems and many branches; usually over 10 feet tall.

Unisexual flower: an imperfect flower; a flower with organs of only one sex present.

Vessels: large-diameter tubes in the wood of hardwood, or angiosperm, trees that carry water from the roots to the trees.

Xylem: the wood of a tree, made up of strong fibers, tracheids and vessels.