Plant Science Terms - R

Raceme - flower stalk on which the florets start blooming from the bottom of the stem and progress toward the top

Rachis - rachis is the midrib of a leaf. It is usually continuous with the petiole and is often raised above the lamina or leaf blade. On a compound leaf, the rachis extends from the first set of leaflets (where the petiole ends) to the end of the leaf. The stem of a plant, especially a grass, bearing flower stalks at short intervals

Radial spacing - horizontal spacing of branches around a trunk

Radicle - root portion of an embryo

Raking, power - removal of debris with rapidly rotating vertical tines or brush

Ray flowers - composite flower head of the daisy family any of a number of strap-shaped and typically sterile florets that form the ray. In plants such as dandelions, the flower head is composed entirely of ray flowers (also called florets)

Receptacle - base of the flower stalk that holds the sexual organs of a flower

Region of maturation - area of the root where the enlarged root cells turn into the various root tissues

Regulatory insect - term used to describe insects that have an unknown impact in a new environment to which they may be moved

Relative humidity - percentage of moisture saturating the air at a given temperature. The ratio of water vapor in the air to the amount of water the air could hold at the current temperature and pressure

Repotting (or “transplanting”) - process of moving previously potted plants into new containers, usually of larger size

Resistance - ability of a host plant to prevent or reduce disease development by retarding multiplication of the pathogen within the host

Respiration - chemical process of burning sugars to use as energy for plant growth. The process by which carbohydrates are converted into energy. This energy builds new tissues, maintains the chemical processes, and allows growth within the plant

Rest - state of suspended growth or outwardly visible activity due to internal physiological factors. Also referred to as physiological dormancy

Retuse - rounded apex with a shallow notch

Reversion growth - stem that originates from and has the characteristics of the plant’s rootstock. (See also Sucker)

Rhizobia bacteria - bacteria that live in association with roots of legumes and convert atmospheric nitrogen to plant-available forms, a process known as nitrogen fixation

Rhizome - underground, horizontal stem that forms the main axis of the plant. This creeping, underground stem produces roots and shoots at each node, serve as storage organs, and a means of vegetative reproduction. (adj. rhizomatous)

Rhizosphere - thin layer of soil immediately surrounding plant roots

Right Place, Right Plant - planting philosophy for a garden relying on plants that are best suited to specific locations in your garden making it much easier to have a successful garden and will generally lower input of time and chemicals

Ringspot - chlorotic or necrotic rings or arcs surrounding healthy tissue

Root - underground vegetative plant part that anchors it into soil and absorbs water and minerals, solution, and often stores food

Root bound - condition in which a plant’s root system has outgrown its pot causes roots to circle around the edges of the pot resulting in root constriction. Further growth is prevented until the plant is removed from the container. To encourage good root growth cut or break up the roots to separate them

Root cap - protective covering over root tips. These specific plant cells protect the root tip as it pushes through the soil. These cells slough off and are replaced by others as roots grow downward

Root cutting - cuttings made from root sections of a plant during the fall or winter. This is a asexual method of propagation that involves removing a section of root from a 2-3 year-old plant during the dormant season and placing it into growing medium

Root galls - swellings on root tissue

Root hair - thin hair-like projection of a root's epidermal cell that which increases surface area for absorption of water and minerals from the soil

Root knots - swelling and deformation of roots

Root meristem - type of apical meristem located at the tips of roots. Provides for elongation of the roots and produces the cells that will become the epidermis, cortex, xylem, cambium, and phloem of the mature root

Root pruning - cutting or removal of some of a plant’s roots

Root/stem rot - fungal disease caused by several different types of fungi where roots of a plant disintegrate or exterior surface pulls away on contact. In addition the roots turn brown to grey, soft, and slimy. It is is often caused by chronic overwatering and impairs a plants ability to uptake water and will often kill plants that are infected.  The most common symptom of root rot is a plant that is wilting even though the soil is wet

Root sucker - see Sucker

Rootstock - portion of a plant used to provide the root system and sometimes the lower part of the stem for a grafted plant

Rosette - small cluster of leaves radially arranged in an overlapping pattern

Rot - decomposition and destruction of tissue

Rotation (rotate) - practice of growing different plants in different locations each year to prevent the buildup of soil borne diseases and insect pests

Row cover - sheet of synthetic material used to cover plants in order to retain heat and exclude insect pests

Rugose - wrinkled

Rogue - uproot or destroy diseased or atypical plants

Runner - slender stolon with elongated internodes. They root at the nodes that touch the ground. see Stolon. (Examples: strawberries and running grasses)

Russet - yellowish-brown or reddish-brown scar tissue on the surface of a fruit. Also naturally occurring tissue on potato tubers.

Rust - fruiting structure of certain family of fungi that requires two hosts. Raised pustules on leaves, stems, and fruits; contain yellow-orange or rust-colored spore masses


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