Chapter 27: Seedless Plants
Heterospory
certain ferns and club mosses (known as spike mosses) exhibit this condition, in which they produce two types of spores: microspores and megaspores.
alternation of generations
clearly defined in plants; the process during which plants spend part of their lives in a multicellular haploid stage and part in a multicellular diploid stage.
bryophytes
consist of about 16,000 species of mosses, liverworts, and hornworts; the only living nonvascular plants.
rhizoids
each individual gametophyte plant has these tiny, hairlike absorptive structures.
Strobilus
each reproductive branch of a horsetail bears a terminal conelike _______.
Polyploids
ferns are interesting research plants for studies in genetics because they are these, having multiple sets of chromosomes. (Many ferns have hundreds of chromosomes).
Microspores
formed when microsporocytes (microspore mother cells) undergo meiosis; each one of these microscopic, haploid structures develops into a male gametophyte that produces sperm cells within antheridia.
Plant megafossils
fossilized roots, stems, leaves, and reproductive structures; currently the oldest known ________ of early vascular plants are from Silurian (420 mya) deposits in Europe.
phloem
one of two vascular tissues; it conducts dissolved organic molecules such as sugar.
xylem
one of two vascular tissues; it conducts water and dissolved minerals
Photoperiodism
plant responses to varying periods of night and day length is referred to as this.
Monophyletic group
plants are described as this; that is, all plants probably evolved from a common ancestral green alga.
Megasporangia
produce megasporocytes (also called megaspore mother cells).
sporophyte generation
produced when two gametes fuse; the diploid portion of the life cycle that produces haploid spores (the first stage in the other of the two generations) by meiosis.
archaeplastids
red algae, green algae, and land plants are collectively classified as this.
Microsporangia
sporangia that produce microsporocytes, also called microspore mother cells, which undergo meiosis to form microscopic, haploid microspores.
Sporangium
spores formed within each of these structures when meiosis occurs.
archegonia
Gametophytes also produce these female gametangia, each bearing a single egg.
wyrt
the Old English word meaning plant from which the suffix "wort" is derived.
Apical meristem
the area at the tip (apex) of a root or shoot where growth - cell division, elongation, and differentiation - occurs.
Anthoceros natans
the common hornwort, within which archegonia and antheridia are embedded in the gametophyte thallus rather than on Archegoniophores and Antheridiophores.
Marchantia polymorpha
the common liverwort; it is thalloid.
Homospory
the condition in which plants only produce one type of spore as a result of meiosis; it is characteristic of bryophytes, horsetails, whisk ferns, and most ferns and club mosses.
Prothallus
the fern gametophyte that lacks vascular tissues and has tiny, hairlike, absorptive rhizoids to anchor it.
Rhizome
the fern sporophyte consists of this horizontal underground stem that bears leaves (fronds) and true roots.
antheridia
the haploid gametophytes produce these male gametangia, in which sperm cells form.
gametophyte generation
the haploid portion of the life cycle is given this name because it gives rise to haploid gametes by mitosis.
Frond
the leaf or leaflike part of a palm, fern, or similar plant.
spores
the mature sporophyte has special cells called sporogenous cells (spore-producing cells, also called spore mother cells) that divide by meiosis to form these haploid structures.
Wattieza
the name given to the treetops of the oldest known megafossils of fernlike trees before they were realized to be part of an entire tree (including the trunks, Eospermatopteris).
Aglaophyton
the new genus into which R. major was reclassified.
gametangia
the sex organs; on most plants, they're multicellular, whereas those of algae are unicellular.
Sphagnum
Commercially, the peat mosses in this genus are the most important mosses; one of the distinctive features of this genus' "leaves" is the presence of many large, empty cells that absorb and hold water. This feature makes peak moss a useful packing material for shipping live plants as well as a good soil conditioner. Added to sandy soils, for example, peat moss helps absorb and retain moisture.
Apical cell
Ferns and other seedless vascular plants have a single large one of these located at the center tip of the apical meristem.
embryophytes
Many botanists refer to land plants as this.
peat
Over time, the organic material compresses to form this.
thallus
The body form of liverworts is often this flattened, lobed structure.
calyptra
The caplike structure that covers the capsule of some species; it is derived from the archegonium.
plant
a complex multicellular eukaryote that has cellulose walls, chlorophylls a and b in plastids, and starch as a storage product that may have cells with two anterior flagella.
Physcomitrella patens
a particularly important research organism for studying plant evolution because its features and genome can be compared with those of algae and flowering plants.
Rhynia major
a plant that grew about 50 cm (20 in.) tall and probably lived in marshes was considered by botanists for many years a classic example of a rhyniophyte. Fossils indicate that this plant had rhizoids, dichotomously branching rhizomes, and upright stems that terminated in sporangia. However, recent microscopic studies of fossil rhizomes indicate that the central core of tissue lacked the xylem cells characteristic of vascular plants, so ___________ was reclassified into a new genus, Aglaophyton, and is no longer considered a rhyniophyte.
Psilotum nudum
a representative whisk fern that has both a horizontal underground rhizome and vertical areal stems.
lignin
a strengthening polymer in the walls of cells that function for support and conduction; production of this was a key step in the evolution of vascular plants.
Indeterminate growth
a unique feature of hornworts is that the sporophytes, unlike those of mosses and liverworts, continue to grow from their bases for the remainder of the gametophyte's life. What is this characteristic called?
Hornwort
after fertilization and development, the needlelike sporophyte projects out of the gametophyte thallus, forming a spike or "horn," hence the name.
charophytes
also known as stoneworts; structural and molecular data indicate that land plants probably descended from this group of green algae.
Drosophila
an important model organism for studies of animal inheritance, development, and evolution; in some ways equivalent to Physcomitrella.
Fiddlehead
as each young frond first emerges from the ground, it is tightly coiled and resembles the top of a violin, hence this name.
Diploid
gene expression in ferns is exactly what one would expect of this sort of plant.
protonema
if a moss spore lands in a suitable spot, it germinates and grows into this filament of cells.
embryo
in plants the fertilized egg develops into this multicellular structure (young plant) within the female gametangium; this last character is one that distinguishes plants from green algae.
Antheridiophores
in some liverworts the gametangia are borne on these stalked structures, which bear antheridia.
Archegoniophores
in some liverworts the gametangia are borne on these stalked structures, which bear archegonia.
Hornworts
located within phylum Anthocerophyta, these are a small group of about 100 species of bryophytes whose gametophytes superficially resemble those of the thalloid liverworts. They live in disturbed habitats such as fallow fields and roadsides.
liverworts
located within phylum Hepatophyta, these consist of about 6000 species of nonvascular plants with a dominant gametophyte generation, but the gametophytes of some liverworts are quite different from those of mosses.
Horsetails
located within phylum Pteridophyta and about 300 mya, these were among the dominant plants and grew as large as modern trees. Because they contributed to Earth's vast coal deposits, these ancient horsetails, like ancient club mosses, are still significant today.
Whisk ferns
located within phylum Pteridophyta, only about 12 species of these exist today, and the fossil record contains several extinct species.
Sori
many species bear the sporangia (located on the fronds) in these clusters.
Club mosses
members of phylum Lycopodiophyta; these were important plants millions of years ago, when species that are now extinct often reached great size.
Ferns
members of phylum Pteridophyta; most of the 11,000 species of these are terrestrial, although a few have adapted to aquatic habitats.
Lycopodium
one of about 1200 or so species of club mosses that are living today; small (less than 25 cm, or 10 in., tall), attractive plants common in temperate woodlands.
capsule
one of the three main parts of the sporophyte; it contains sporogenous cells (spore mother cells).
seta
one of the three main parts of the sporophyte; known as the stalk.
foot
one of the three main parts of the sporophyte; this structure anchors the sporophyte to the gametophyte and absorbs minerals and nutrients from it.
Eospermatopteris
the trunks of the oldest known megafossils of fernlike trees were given this name when they were discovered in the late 1800s; not until 2007 was a fossil of an entire tree pieced together. The treetops had previously been found separate from the trunks and named Wattieza.
Psilotum
the upright stems of these are green and are the main organs of photosynthesis.
Megaspores
these haploid structures are formed when megasporocytes undergo meiosis; each of these develops into a female gametophyte that produces eggs in archegonia.
Megaphylls
these structures probably evolved from stem branches that gradually filled in with additional tissue (webbing) to form most leaves as we know today; these have more than one vascular strand, as we would expect if they evolved from branch systems.
leafy liverworts
these superficially resemble mosses, with leaflike blades, "stems," and rhizoids rather than a lobed thallus.
zygote
this is formed when sperm cells reach the female gametangium from one of many ways, and one sperm cell fertilizes the egg.
cuticle
this waxy structure covers the aerial portion of a plant; an important difference between plants and algae.
Gemmae
tiny balls of tissue formed by some liverworts that allow them to reproduce asexually; borne in the saucer-shaped structure, the gemmae cup, directly on the liverwort thallus.
stomata
tiny pores which dot the surfaces of leaves and stems of almost all plants that facilitate gas exchange.
Microphyll
usually small and has a single vascular strand; probably evolved from small, projecting extensions of stem tissue (enations); only one group of living plants, the club mosses, have these.
Rhynia gwynne
vaughanii - an example of an early vascular plant that superficially resembled whisk ferns in that it consisted of leafless upright stems that branched dichotomously from an underground rhizome; it lacked roots, although it had absorptive rhizoids.
Dichotomous branching
whenever the stem forks, or branches, it always divides into two equal halves through the process of _________ _________.