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Plants |
| PLANTS | Glossary R-S |
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| Palæos: | |
Plants |
| PLANTS | Glossary R-S |
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Unit Cladogram |
||
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Rhizoid: hair-like filamentous projection for anchorage or absorption.
Rhizome:
a (usually) underground stem that is horizontally oriented; rhizomes may appear
like roots, but have a definite node and internode architecture. Image from the
site: Flora of
Roosevelt Monmouth County, New Jersey by Ross Tulloss & Mike
Hamilton.
Root: a plant organ that functions in anchorage and absorption; in seed plants derived from a bipolar embryo
Saccate pollen: pollen with a saccus or sacci; characteristic of many conifers. See image at bisaccate.
Saccus: ( pl. sacci) a wing-like or bladder-like extension on a pollen grain. See image at bisaccate.
Sclerenchyma: tissue composed of cells with walls thickened with lignin; sclerenchyma tissue functions primarily in strengthening and support
Sclerotesta:
the middle, fibrous layer of the integument in some seeds. Image from Dunn
et al. (2002) showing cross sections of a Rhynchosperma quinii seed
from the late Mississippian
(Serpukhovian?)
of Arkansas.
Secondary growth: growth in width initiated and maintained by the vascular cambium and cork cambium. See cambium. The vascular cambium surrounds the core of the stem, branch or root. It creates xylem medially and phloem radially. If present, the cork cambium, a second, outer layer of cambium, creates a new outer layer (typically bark) radially.
Secondary phloem: phloem produced by the vascular cambium. See phloem, cambium, secondary growth.
Secondary xylem xylem produced by the vascular cambium. See xylem, cambium, secondary growth.
Seed: a fertilized ovule; megasporangium that contains an embryo enclosed in an integument. A seed has been described as "a baby sporophyte in a jacket with a lunch sack." Gymnosperm Evolution. The advantage of a seed is that it can combine the dispersal functions of a spore with sexual reproduction.
Seed
fern: any of a number of extinct seed-bearing plants with fern-like
leaves. Image of Neuropteris from the Kentucky
Paleontological Society web site.
Seed plants: a monophyletic clade of plants that reproduces by seeds; megagametophyte is retained on the parent sporophyte and enclosed in an integument; microgametophyte is transferred to the megagametophyte.
Sepal: a whorl of a flower; sepals often resemble reduced leaves and function in the protection of the bud; sepals may be modified to function more like a petal.
Seta: This incredibly over-used anatomical term is simply Latin for a bristle or a stiff hair. It is used in a variety of contexts, not only for things that look like bristles (or, to be sure, stiff hairs), but also for things like the stalk of the sporophyte in mosses, which looks nothing like a bristle (or, for that matter, a stiff hair).
Simple tissue: tissue composed of only one cell type
Sinus: the indentations of a lobed pinna or pinnule of a fern or of a dicot leaf.
Solute: anything dissolved in a solvent. In salt water, the water is the solvent, and the salts are solutes.
Sorus:
(pl sori) a cluster or group of sporangia of a fern; most
frequently applied to clusters of fern sporangia attached to the bottom of fern
leaves. Image from the
General
Biology Lab site by Diane Jokinen and Patrick Duffie of Loyola
University Chicago.
Sporangiophore: modified branch on which the sporangium is attached.
Sporangium: (pl. sporangia) hollow, unicellular or pluricellular structure in which spores are produced.
Spore: a haploid (1N) reproductive cell capable of developing directly into a gametophyte without uniting with another cell.
Sporophyll: a spore-bearing leaf; a modified leaf bearing sporangia.
Sporophyte: the spore producing, diploid (2N) phase of the life cycle; compare to gametophyte.
SSU rDNA: DNA coding for RNA associated with the small ribosomal subunit, i.e. for "18S" RNA.
Stamen: the "male" structures of a flower, consisting of a supporting filament and the anther, a sac which produces and holds the microgametophytes (pollen).
Stele: vascular tissue (the xylem and phloem together); the central vascular cylinder in stems and roots where the vascular tissue is located.
Stem: same as axis; a plant axis with leaves or enations.
Stigma: (pl. stigmata) the distal part of the pistil, the organ that receives the pollen. Stigmata may be quite varied in shape and structure. They are often button-shaped and studded with hair-like papillae ("dry" stigmata) or coated with a sticky film ("wet" stigmata) to capture pollen.
Stoma:
(pl. stomata) tiny pores or opening in the epidermis
of leaves; stomata are flanked by two guard
cells that regulate opening and closing of the pore and thus regulate gas
exchange (respiration) and transpiration. Image from the Ecotree
site by Martin Cocks of the University of the Western Cape (South Africa).
Strobilus: (pl. strobili) a cone a cone-shaped cluster of spore-bearing leaves (e.g., a pine cone), an aggregation of sporophylls on a common axis.
Suberin: waxy, waterproof chemical in some plant
cells, notably cork (in stems) and endodermis cells (in roots). Suberin
is an extremely complex and irregular material, like lignin
-- with which it shares some similarities. Suberin is composed of two
physically separated domains: the aliphatic and phenolic. The phenolic
domain is rather lignin-like, but with even greater variability, and built on
the same basic unit of a di- or tri-hydroxyphenyl group attached to a
three-carbon chain, variously oxidized and integrated with the carbohydrates of
the cell walls. Perhaps the most common building block is ferulic acid:
formally, 3-(2'-methoxy-3'-hydroxyphenyl)-propenoic acid. Distally, the
phenolic domain is attached at points by ester 
linkages to glycerol. The
remaining hydroxyls of the glycerol molecule are ester-linked to some
strange-looking C-18 to C-30 lipids. These lipids are substituted at C9-10
with one or two hydroxyls, or even with an epoxide link between the two
carbons. Finally the ω- position may be oxidized to a
carboxylate (alone or esterized to glycerol) or hydroxyl (alone or esterised to
ferulic acid). Variations allow for cross-linkage to other suberin
molecules via the 9-10 or ω positions. Image adapted from Bernards
(2002).
Style: a tubular column in the pistil of a flower, through which the pollen is transported from the stigmata to the ovary.
Succulent: a plant that is able to store water in its tissues and then withdraw it during times of drought. e.g. a cactus. The water storage tissue may be found in the stem, leaves, or roots depending on the species. Stem succulents, leaf succulents, and root succulents are types of growth forms.
Synangium: (pl. synangia) a reproductive unit composed of fused sporangia.
Synapomorphy: a unique character which is shared by all basal members of a clade and is derived from their common ancestor, but not shared with ancestral groups. A synapomorphy may be secondarily lost in later descendants. Only a synapomorphy may be used to infer phylogeny.
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