The plant calibration species are a set of 20 plants selected to help "calibrate" phenological measurements across the USA. These native and introduced plants have broad distributions and are ecologically or economically significant. Observations on calibration species will be integrated to get "the big picture" regarding plant response to environmental change. Observers are encouraged to include at least one calibration species in their monitoring projects. Widespread observation of calibration species helps integrate collective plant data with climate change measurements nationwide.

The outer whorl of the flower's perianth and the collective terminology for all of the sepals of a flower; typically green and which often protect the flower bud

A cylinder of meristematic plant tissue (lateral meristems) of many woody seed-bearing plants, producing new xylem towards the inside of a plant (stem, root) and new phloem to the outside of a plant (stem, root). The vascular cambium forms tissues, xylem and phloem, that carry water and nutrients throughout the plant. Addition of the new tissue causes the diameter to increase. The cork cambium creates cells that eventually become bark on the outside and cells that add to the cortex on the inside.

A layer of vegetation elevated above the ground. It can refer to the layer of leaves surrounding an individual tree or shrub, or to the continuous layer of vegetation that comprises the top layer of a forest.

The tree species that comprise a forest canopy

A tightly clustered inflorescence of unstalked flowers, sometimes flat (like daisies or dandelions) or globular (like buttonbush)

A dry, dehiscent fruit that has developed from one flower having a single ovary divided into several carpels - often fused, and splitting open along a seam of the carpel or opening at pores at maturity.

The simplest unit within a pistil (ovary, style, stigma). A simple pistil has one carpel (ovary, style, stigma) or a compound pistil has multiple carpels (each having an ovary, stigma, style - joined in various ways)

A grain, such as for grasses; a dry, indeshiscent fruit that has developed from one flower having a single ovary, where the seed coat is fused to the ovary wall.

A small, modified leaf or bract that can surround vegetative or floral meristems (buds and growing points), or occur on a rhizome; commonly providing protection

An inflorescence (cluster of flowers) consisting of a dense spike or raceme of apetalous, unisexual flower as in Salicaceae and Betulaceae; an ament (a cylindrical flower cluster).

A membrane-bound body found within a cell's cytoplasm that performs specific cellular functions

The minimum period of cold weather needed, after which a fruit-bearing tree will blossom. It is often expressed in hours

The organelle within the cell which contains chlorophyll, and is necessary for photosynthesis to occur (see photosynthesis)

An organized structure of DNA, protein, and RNA found in cells. It is a single piece of coiled DNA containing many genes

A flattened, leaf-like stem or branch which functions like a leaf

A group of individuals originating from a single parent plant through vegetative reproduction.

A group of individual plants all originating by vegetative propagation (asexual) from a single plant, and therefore genetically identical to it and to one another

To reproduce or propagate asexually. 

Genetically identical plants. The cloned plant component of the USA-NPN Plant Phenology Program offers monitoring of a small group of species, including the cloned lilac,that will eventually be distributed nationwide.

A plant that has originated by vegetative propagation (asexual) from another plant, and therefore is genetically identical to it

In monocotyledons/monocots, the first leaf following the cotyledon, which forms a protective sheath around the plumule/stem tip

A flower having all the whorls of principal parts: sepals, petals, stamens and pistils

A leaf blade that is divided into separate leaflets

A hard and dry part that is the fruit of a pine tree or other evergreen plant and contains many seeds.

A plant species that does not flower and instead bears cones (or strobili)

Bearing cones or strobili.

A root that can shorten itself, pulling the plant deeper into the soil. They typically have a wrinkled surface that serves for expanding and contracting

A short, solid, underground stem having thin, papery leaves that surround a bud/meristematic region, such as an

A small corm that arises from the base of a larger corm, generated by asexual reproduction

The inner whorl of the flower's perianth and the collective terminology for all of the petals of a flower; typically colored, petals separated or joined (connate), and commonly advertising a flower's sexual readiness

In roots and stems, the tissue between the stele (primary vascular structure and tissues) and the epidermis

seed leaf; embryonic leaf; the first leaf or one of the first pair of leaves to develop in a seed plant. Cotyledons, when they emerge with seedling shoot, do not look the same as the plant’s “true leaves,” which develop after germination.

The hollow or pithy stem which bears the inflorescences/flower heads, found in grasses, sedges, and rushes

A cultivated variety of a plant that has been deliberately selected for specific desirable characteristics (such as the colour and form of the flower, yield of the crop, disease resistance, etc.).

The cupule holds and protects the seed during its growth and maturation. In some genera it only partly encloses the single nut, while in others, it fully encloses the two or more nuts, and splits open at maturity into four valves to release the nuts. The cupule is covered by numerous scales. In some species the scales are developed into sharp spines, giving the nut protection from squirrels and other seed predators.

The waxy, waterproof layer on the surface (and covering the epidermal cell layer) of plant leaves and stems