Glossary for Gardeners – R

Glossary for Gardeners

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~ R ~

raceme
A flower stalk on which the florets start blooming from the bottom of the stem and progress toward the top.
radial spacing
The horizontal spacing of branches around a trunk.
radicle
The first part of a seedling to emerge from the seed. Grows downward and develops into the primary root.
raphide
A needle-shaped crystal of calcium oxalate in certain species’ cells that deter herbivores.
ray flower
One of several small flowers often forming a ring around the disc flowers in a composite head.
receptacle
The enlarged end of a flower stalk to which the flower parts are attached.
recessive trait
A genetic characteristic that is masked by a dominant gene.
relative humidity
The ratio of water vapor in the air to the amount of water vapor the air could hold at the current temperature and pressure.
resin
A viscous, protective secretion of many conifers that is insoluble in water and hardens in contact with air.

resistant
A plant having qualities that make it retard the activities of a pathogen or insect pest. See immune, tolerant.
respiration
The process within plants where sugars and starches are converted into energy.
reticulate venation
A net-like vein pattern in some leaves.

reversion growth
A stem that originates from, and has the characteristics of, the plant’s rootstock. See sucker.
Rhizobia bacteria
Bacteria that live in association with the roots of legumes and convert atmospheric nitrogen to plant-available forms, a process known as nitrogen fixation.

rhizome
A thickened underground stem that grows horizontally with bud eyes on top and roots below. Bearded iris is an example of a plant that produces rhizomes.
rhizosphere
The thin layer of soil immediately surrounding plant roots.
ribosome
A celluar organelle which is the site of protein synthesis.
ripeness-to-flower
The minimum vegetative size a plant must achieve before it is capable of flowering.
root
Generally, the underground portion of a plant. It anchors the plant and absorbs water and nutrients.
root cap
A protective cover over a root tip.
root cutting
A section of root prepared for the purpose of vegetative propagation.
root hair
A delicate, elongated epidermal cell that occurs just behind a root’s growing tip. Root hairs increase the root’s surface area and absorptive capacity.
root nodule
A small swelling on a root resulting from invasion of nitrogen-fixing bacteria.
root pressure
The pressure developed by living cells in the root pushing water up the xylem.
root pruning
The cutting or removal of some of a plant’s roots.
root tuber
An enlarged, food-storage root bearing adventitious shoots.
root-bound
A condition in which a plant’s roots have completely filled its container. Typically, the roots begin to encircle the pot’s outer edge. Further growth is prevented until the plant is removed from the container.

rootstock
The root or stem onto which a scion or interstock is grafted.
rosette
A small cluster of leaves radially arranged in an overlapping pattern.
rot
Decomposition and destruction of tissue.
rotation
The practice of growing different plants in different locations each year to prevent the buildup of soil-borne diseases and insect pests, or the depletion of specific nutrients.
row cover
A sheet of synthetic material used to cover plants in order to retain heat and exclude insect pests.
rugose
Wrinkled.
runner
See stolon.
russet
Yellowish-brown or reddish-brown scar tissue on a fruit’s surface.