Plant Science Terms - T

Taproot - type of primary root system that grows straight down with few lateral roots, persists, and maintains its dominance

Taxonomist - scientist whose job it is to classify plants, or other organisms, into their correct scientific classifications.  With DNA sampling, more exact classification is possible

Taxonomy - classification or naming of plants or animals

Temperate fruit - fruit plant that requires a cool period and is deciduous. Examples are apple, pear, and peach

Temporary branch - small shoot or branch left on a young tree’s trunk for protection and nourishment; low lateral allowed to remain until a tree is tall enough to have scaffolds at the desired height

Tender - not tolerant of frost and cold temperatures. In horticulture, tender does not mean weak or susceptible to insect pests or diseases

Tender Perennial/Temperennial - Plants that are perennial in warm locations but are not winter hardy in cold locations.  These plants are often treated as annuals in cold climates or may be in the house plant section

Tendril - slender, twining leaf modifications used for support and clinging, usually a modified leaf. Easily seen on vines such as grapes and clematis

Terminal - tip (apex), usually of a branch or shoot

Terminal bud - large and vigorous buds found at the tip of stems, responsible for terminal growth

Thatch - tightly intermingled layer of undecomposed roots, stems, and shoots located between the soil surface and the green vegetation of the turf grass. The brown, fibrous, spongy layer located between the soil and the grass blades

Thermoperiod - change in temperature from day to night

Thermophilic - growing at high temperatures, as in microorganisms that break down organic matter in a hot compost pile

Thin - remove an entire shoot or limb where it originates; selectively remove plants or fruits to allow remaining plants or fruits to develop

Thorax - thorax is made up of three segments (prothorax, mesothorax, and metathorax). Each segment has a pair of legs, and the wings are attached to the last two segments, which also have spiracles or circular openings used for breathing

Thorn - short, hard, sharp-pointed, leafless branch. A modification of a stem or branch which means they can be branched or not, have leaves or not and they arise from a bud. A black locust tree (Robinia pseudoacacia ) or hawthorn (Crataegus oxycantha) is an example of a plant that produces thorns. (See Prickle)

Threshold - point at which plant aesthetic quality or injury leads a gardener to decide action should be taken

Thriller - plants that are placed in the center or back of a combination planter to add drama and height to the combination

Thysanoptera - major order of insects that have two pairs of wings, or are wingless, and rasping-sucking mouthparts (thrips)

Thysanura - major order of insects that are wingless and have chewing mouthparts (silverfish, firebrats)

Tiller - grass plant shoot arising in the axes of leaves in the unelongated portion of the stem. A shoot that arises from a plant’s crown

Tilth - state of aggregation of a soil especially in relation to its suitability for crop growth

Time Release Fertilizer - fertilizer that comes in pellets and is released based on soil temperature itself (not microbe action) and tends to be more exact than Slow Release Fertilizer. It is an improved version of Slow Release Fertilizer (Also called Controlled Release Fertilizer)

Tip layering - layering in which rooting takes place near the tip of the current season's shoot, which naturally falls to the ground

Tissue culture - process of creating new plants by placing small pieces of plant material onto a sterile medium (agar or in liquid suspension) and growing masses of unorganized cells. Useful for the rapid asexual multiplication of plants

Tolerant - plant that will produce a normal yield even if infested by a disease or insect pest

Tomentose - leaf textures that are covered with matted, wooly hairs; Example: Lamb’s Ear 

Top-dressing - practice of spreading a thin layer (14 inch) of soil, compost, humus, or a sand and peat mix over the turf or soil. 2) For turf: A sand or prepared soil mix applied to the turf to help smooth the surface, enhance establishment, and reduce thatch buildup

Topiary - tree or shrub shaped and sheared into an ornamental, unnatural form, usually a geometric shape or the shape of an animal

Topsoil - upper layer of soil that you plant in.  It varies in depth from place to place, but will almost always be less than a foot deep and can be as little as 2 inches deep

Topworking - grafting procedure by which branches of trees are changed to a more desirable cultivar

Totipotency - ability of any cell to develop into an entire plant

Toxicity - when a plant does not react well to something it is often called Toxicity.  Toxicity could refer to too much fertilizer, too much sun, sensitivity to insecticides etc.

Trace element - nutrients that plants need in small amounts. These elements are usually included in most commercial fertilizers. Common trace elements include Boron, Copper, Iron, Manganese, Molybdenum, and Zinc. see Micronutrient

Tracheophytes - plant that has elaborate tissues with water- and nutrient-conducting tissue termed “vascular tissue” including roots, stems and leaves. Some tracheophytes reproduce with seeds and some with spores

Trailing - plants that trail along the ground or out of pots but do not root at nodes along the stem and are not self­ supporting and have low yields. Examples: cane berries

Transpiration - loss of water vapor from plants through the leaf stomata. The transpired water comes from the photosynthetic process and also from water in the cells

Trap Crop - plant that attracts agricultural creatures usually insects, away from nearby crops. This form of companion planting can save the main crop from decimation by pests without the use of pesticides

Tree - woody plant with a single stem and branches that begin some distance from the ground.  They are relatively large, especially when compared to shrubs 

Triadic - use of three colors that are at equal distances from each other on the color wheel

Trichomes - “hairs” that are extensions of the epidermal cells on a leaf

Trickle irrigation - application of small quantities of water directly to the root zone through various types of delivery systems on a daily basis

Tropism - tendency of a plant part to turn in response to an external stimulus, either by attraction or repulsion, as a leaf turns toward light. (See Geotropism, Phototropism)

True leaves - first leaves to emerge after the germination of a seed

Truncate - having a relatively square end to a leaf margin

Trunk - main stem of a tree. Also called a bole

Trunk taper - degree to which a tree's stem or trunk decreases in diameter as a function of height above ground

Truss - flower cluster, usually growing at the terminal of a stem or branch

Tuber - enlarged, underground stem used for food storage of starch or related materials such as a potato; for turf it is an underground stem modified for food storage that is attached to the root system such as in yellow nutsedge

Tuberous root - underground storage organ made up of root tissue. Sprouts only from the point at which it was attached to the stem of the parent plant. Dahlias are an example

Tuberous stem - below ground stem consisting of a swollen hypocotyl, lower epicotyl, and upper primary root (for example, in tuberous begonias)

Tunicate - tunicate bulb has a paper-like covering or tunic that protects the scales from drying and from mechanical injury. Examples of tunicate bulbs include: tulips, daffodils, hyacinths, grape hyacinths (muscari), and alliums

Turf - covering of mowed vegetation, usually a grass

Turfgrass - species or cultivar of grass, usually of spreading habit, which is maintained as a mowed turf

Tolerance, turf - ability of a turf species to withstand application of a pesticide (herbicide) at the normal dosage without being killed or injured. Specific tolerance may be associated with an anatomical or physiological characteristic in the plant

Turgor or turgor pressure (turgid) - cellular water pressure; responsible for keeping cells firm

Twig - young stem (1-year-old or less) that is in the dormant winter stage (has no leaves)


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