| Root: | an absorbing and anchoring organ developing from the radicle and usually positively gravitropic |
Root Apical Meristem Vocabulary
[See Cytology and Meristems Vocabulary]
Embryonic Root Vocabulary
[See Seeds and Seedlings Vocabulary]
Mature Root/Stem Parts
| Aerenchyma: | a parenchyma tissue with very large gas spaces forming passage canals for gas exchange, common in roots of plants living in swampy soils |
| Cambium= vascular cambium: | a residual (lateral) meristem arising from an apical meristem and giving rise to secondary xylem and secondary phloem |
| Casparian Strip: | a waxy, waterproofing deposit in the radial and transverse walls of endodermal cells |
| Companion Cell: | small-diameter parenchyma cell in the phloem associated with sieve tube members and providing for their needs through plasmodesmata |
| Cortex: | a ground tissue layer between the epidermis and the vascular tissues |
| Endodermis: | a parenchyma layer outside (and sometimes in stems also just inside) the vascular tissue, having Casparian strips, and responsible for selective mineral uptake |
| Epidermis: | the exterior parenchyma layer of roots, stems, and leaves |
| Hypodermis: | a suberized layer of cells just under the epidermis, common in mature roots growing in arid soils |
| Metaxylem: | primary xylem consisting of vessels; maturing after protoxylem |
| Pericycle: | a parenchymatous layer just inside the endodermis, producing branch (secondary) roots in all species, and periderm in woody species |
| Pith: | a tissue region inside the vascular tissues usually consisting of parenchyma, but perhaps also including hollow air-space |
| Primary Phloem: | phloem tissue originating from a provascular tissue |
| Primary Xylem: | xylem tissue originating from a provascular tissue |
| Protoxylem: | primary xylem consisting of tracheids; the first to form from provascular tissue |
| Root Hair: | an extension of an epidermal cell, growing out into soil particles and responsible for water and mineral intake |
| Secondary Phloem: | phloem tissue originating from the vascular cambium and maturing to its outside |
| Secondary Xylem: | xylem tissue originating from the vascular cambium and maturing to its inside; wood |
| Sieve Tube Member/Element: | elongate thin-walled, but large-diameter cells in the phloem transporting organic solutes usually from leaves to the rest of the plant; alive but lacking nucleus, plastids, mitochondria, etc. |
| Stele: | the combined tissues inside the cortex, in roots the pericycle, xylem, phloem, and any pith present. |
| Tracheid: | a spindle-shaped cell transporting water and minerals in the xylem, with end walls; dead at maturity |
| Velamen: | a multiple epidermal system responsible for water intake from mist, yet reducing water loss in aerial roots |
| Vessel: | a tube-like cell transporting water and minerals in the xylem, lacking end walls or having perforated end walls; dead at maturity |
Xylem/Phloem Arrangements
| Bicollateral: | a vascular bundle in which xylem and phloem share two surfaces |
| Collateral: | a vascular bundle in which xylem and phloem share only one surface |
| Radial: | a vascular cylinder with xylem and phloem in alternate ridges (in alternating radii of cross-section) |
Xylem Maturation Patterns
| Endarch: | xylem matures centrifugally; metaxylem is closer to the epidermis than is the protoxylem |
| Exarch: | xylem matures centripetally; protoxylem is closer to the epidermis than is the metaxylem |
| Mesarch: | xylem matures both centripetally and centrifugally; metaxylem appears both interior to and exterior to the protoxylem |
Stele types
| Actinostele: | a protostele with lobed or stellate strand of xylem surrounded by phloem |
| Amphiphloic: | a siphonostele with phloem both on the inside and the outside of the xylem cylinder |
| Diarch: | a stele with two ridges of protoxylem |
| Ectophloic: | a siphonostele with phloem surrounding the outside of the xylem cylinder |
| Eustele: | a dissected siphonostele consisting of collateral or bicollateral bundles |
| Haplostele: | a protostele with xylem completely surrounded by phloem |
| Pentarch: | a stele with five ridges of protoxylem |
| Plectostele: | a protostele with bands of xylem surrounded by phloem |
| Polyarch: | a stele with many ridges of protoxylem |
| Protostele: | consisting of a solid column of vascular tissue |
| Siphonostele: | consisting of a hollow cylinder of vascular tissue; pith occupies hollow portion |
| Tetrarch: | a stele with four ridges of protoxylem |
| Triarch: | a stele with three ridges of protoxylem |
Appendage Origins
| Endogenous: | an appendage arising from internal layers |
| Exogenous: | an appendage arising from dermal and perhaps a few external cortical layers |
Root Interactions
| Ectotrophic: | a symbiosis in which the non-plant haplobiont lives outside the plant cells (but also between plant cells) |
| Endotrophic: | a symbiosis in which the non-plant haplobiont lives inside the plant cells |
| leg-Hemoglobin: | a type of hemoglobin produced by legumes in the external layers of root nodules typically containing Rhizobium bacteria |
| Mutualism: | a symbiosis in which both haplobionts benefit from the association |
| Mycorrhiza: | a fungus-root symbiosis |
| Nodule: | a tumor-like formation in response to the presence of a microorganism, often housing an endotrophic haplobiont |
| Symbiosis: | a close relationship between two species (haplobionts) living in continuous intimate contact with each other |
Root Origins
| Adventitious: | developing from dedifferentiated parenchyma from a structure other than a root |
| Primary: | developing from the apical meristem of the radicle |
| Secondary= lateral: | developing from the pericycle of another root |
Specialized Root Types
| Aerial: | above-ground roots, usually extending into the air |
| Buttress: | roots developing board-like growth on the upper side and assisting with support of the trunk against lateral forces |
| Contractile: | roots capable of shrinking usually drawing the plant deeper in the soil, but in some cases drawing the plant horizontally through the soil. |
| Fibrous: | consisting of fine or threadlike slender roots |
| Fleshy: | succulent roots |
| Haustorial: | roots of parasitic species penetrating into host tissues for nutrient absorption |
| Knee= aerating: | vertical or horizontal above-ground roots, usually involved with plants living in swampy soils |
| Pneumatophorous: | containing spongy aerenchyma tissues of plants living in swampy soils |
| Prop= stilt: | adventitious roots arising at a steep angle from the lower portions of stems and rooting in soil to support the trunk against lateral forces |
| Tap: | a persistent and well-developed primary root. |
| Tuberous: | extremely fleshy roots resembling stem tubers |
This page © Ross E. Koning 1994.
The CBE citation style for this page would be: Koning, Ross E. 1994. "Root Vocabulary". Plant Physiology Website. http://koning.ecsu.ctstateu.edu/plant_biology/rootvocab.html (your visit date)
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