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EnchantedLearning.com Botany and Paleobotany Dictionary

Plants

RACHIS The rachis is the midrib of a leaf. It is usually continuous with the petiole and is often raised above the lamina (the 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.	RADIAL SYMMETRY Radial symmetry is when a basic shape unit is repeated around a central point (for example, most flowers have radial symmetry).	RADICLE The radicle is the lower part of a embryo's axis. The radicle develops into the primary root.
RADIOISOTOPE DATING Radioisotope dating of igneous rock layers is used to find out how old the rock is (when the igneous rock formed). One way of dating fossils is by dating bracketing layers of igneous rock.	RAFFLESIA The Rafflesia flower (Rafflesia arnoldi) is the world's largest flower. This giant bloom is found in rainforests of Indonesia. Locally, it is called the "corpse flower." Rafflesia gives off a putrid smell that reminds people of rotting meat (this odor attracts its pollenators, beetles and flies), hence its nickname. Rafflesia's enormous flower is about 3 feet (1 m) across and weighs about 20 pounds (9 kilograms). The flower takes about a year to develop, then it blooms for about a week before dying. The flower has five wide orange petals (with pale dots) surrounding a spiked cup. Rafflesia has no stem, no roots, and no leaves. The flower is supported by fungus-like tissue that lives in another plant - the Tetrastigma vine.	RAINFOREST Rainforests are very dense, relatively warm, wet forests. They are havens for millions of plants and animals.
RECEPTACLE The receptacle is the terminal portion of the flower stalk.	REDWOOD The redwood is the tallest tree, growing up to 370 feet (113 m) tall and living for over a thousand years. One redwood tree in California is 2,200 years old. The roots of this giant conifer are shallow, but spread sideways up to 250 feet (75 meters) from the trunk. The bark is deeply-furrowed, fibrous, thick [up to about 1 foot (30.5 cm) thick] and lacks resin. There are many species of redwood, including the giant coast redwood, Sequoia sempervirens.	REGRESSION Regression is the exposure of continental land as the sea level decreases, usually caused by increasing polar ice and glacier formation. Another causes is the local uplift of the continental land.
RENIFORM A reniform leaf is kidney-shaped.	REPAND A repand leaf has a wavy margin.	RESIN Resin is a substance secreted by some plants. Resin is often aromatic (having a strong odor); itt is insoluble in water but will dissolve in alcohol. Fossilized resin is called amber.
RESINIFEROUS Resiniferous means producing resin.	C6H12O6 + 6O2 = 6CO2 + 6H2O + ATP RESPIRATION Respiration is a process in which energy is generated in cells. In respiration, glucose (a type of sugar) and oxygen are converted into carbon dioxide, water and ATP (adenosine triphosphate). Respiration takes place in the mitochondrion of both plant and animal cells.	RETICULATE VENATION A leaf with reticulate venation has its veins arranged in a pattern such that larger veins give rise to progressively smaller veins. The end branches of the veins define small areas called aeroles.
RHIZOBIA Rhizobia are bacteria that live symbiotically with plants (especially legumes), living on the plant's roots. The rhizobia fix nitrogen (from atmospheric nitrogen) for the plant and the rhizobia get energy from the plant.	RHIZOME A rhizome is a thick, horizontal underground stem (not a root) of a plant, that grows close to the ground. Rhizomes have nodes and scale-like leaves; roots form on the lower surface and new shoots can form at nodes. Ferns, mosses, horsetails, ginger, irises, and some grasses have rhizomes.	RIBOSOME Ribosomes are small organelles composed of RNA-rich cytoplasmic granules that are sites of protein synthesis.
RIPARIAN FOREST A riparian forest is situated by a river bank or other body of water.	RNA RNA (short for ribonucleic acid) is a complex, organic, single-stranded molecule that is found in the nucleus and the cytoplasm of cells. RNA carries DNA's instructions for chemical synthesis (like protein formation) to the cell and guides the formation of these chemicals. There are many types of RNA that have different functions. The major types of RNA are messenger RNA (mRNA, which carries the information for protein synthesis from the chromosomal DNA to the ribosomes), transfer RNA (tRNA, which translates mRNA and bonds with amino acids to correctly form the desired proteins), and ribosomal RNA (rRNA, found in ribosomes).	ROOT A root is a plant structure that obtains food and water from the soil, stores energy, and provides support for the plant. Most roots grow underground.
ROOT CAP The root cap is a cap-shaped structure at the ends (tips) of the roots. It covers and protects the apical meristem (the actively growing region) of the root.	ROOT HAIRS Root hairs are very thin, hair-like roots that are extensions of the root's epidermis. Root hairs have a large surface area and absorb water and minerals for the plant.	ROOT TIP The root tip is the tip of the root and contains the root cap and the apical meristem (the actively growing region).
ROUGH ENDOPLASMIC RETICULUM Rough ER is a vast system of interconnected, membranous, infolded and convoluted sacks that are located in the cell's cytoplasm (the ER is continuous with the outer nuclear membrane). Rough ER is covered with ribosomes that give it a rough appearance. Rough ER transport materials through the cell and produces proteins in sacks called cisternae (which are sent to the Golgi body, or inserted into the cell membrane).	RUBBER TREE Rubber trees are large trees (belonging to the spurge family, family Euphorbiaceae) that live in tropical (warm) areas. These trees are tapped for their latex (from which rubber is made), which is produced in their bark layers (it is not the sap). The Pará rubber tree (Hevea brasiliensis) is native to South American rain forests, and grows to be over 100 ft (30 m) tall. In 1876, Henry Wickham brought seeds from the Para rubber tree (taken from the lower Amazon area of Brazil) to London, England. Seedlings were grown in London, and later sent to Ceylon and Singapore. The technique of tapping rubber trees for their latex was developed in southeast Asia (before that, the trees were cut down to extract the rubber). Commercial rubber production now takes place in Malaysia, Thailand, Indonesia, and Sri Lanka (but not significantly in South America).	RUGOSE Rugose means ridged, rough, or wrinkled.
RUMINANT A ruminant is an animal that digests its food many times. This food is usually tough plant material like grasses. Ruminants include cows, sheep, antelopes, and camels.	RUNOFF Runoff is water that drains or flows from the land into streams and rivers, eventually into seas. The water is generally from rain or snowpack melt.

Plant Printouts

EnchantedLearning.com Botany and Paleobotany Dictionary

Plants

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