EVOLUTION AND DIVERSITY OF VASCULAR PLANTS
VASCULAR PLANT APOMORPHIES
1. What is the formal, scientific name for the vascular plants?
2. Name the major apomorphies of the vascular plants.
Sporophyte independent, long-lived; sporphyte branched, with multiple sporangia; lignin, in lignified, secondary cell walls; sclerenchyma; vascular tissue, with xylem and phloem; endodermis; roots.
3. What two features of the sporophyte are apomorphic for vascular plants, distinguishing them from liverworts, mosses, and
Sporophyte independent, long-lived and branched, with multiple sporangia.
4. What are two early evolving branching-patterns lineages in the vascular plants?
Dichotomous and pseudomonopodial.
5. How was the evolution of lignin a major adaptive feature of the vascular plants?
Gave structural support to cells, enabling plants to grow taller, bigger, outcompete others.
6. What is the difference between a primary and secondary cell wall in terms of time of deposition and chemistry?
Primary: form during primary growth, as cells are elongating, composed of a primary cell wall of cellulose and pectin.
Secondary: form after cell elongation has ceased, composed of primary and secondary cell walls, the latter containing lignin.
7. What is a pit? What is a primary pit field?
a) A pit is a hole in a secondary cell wall; b) a primary pit field are holes in adjacent primary cell walls.
8. Is the secondary cell wall formed inside or outside the plasma membrane? Is it formed inside or outside the primary cell wall?
It is formed outside the plasma membrane and inside the primary cell wall.
9. What are the general characteristics of sclerenchyma cells?
Nonconductive cells that have a thick, lignified secondary cell wall, typically with pits, and that are dead at maturity.
10. Name the two types of sclerenchyma and state how they differ.
a) fibers, which are long, very narrow cells with sharply tapering end walls, function in mechanical support of organs and tissues.
b) sclereids, which are isodiametric to irregular or branched in shape; may also function in structural support, or possibly help to deter herbivory in some plants.
11. What is the function and structure of tracheary elements?
Tracheary elements are specialized cells that function in water and mineral conduction, and are generally elongate cells, are dead at maturity, and have lignified secondary cell walls.
12. What is xylem?
A tissue composed of tracheary elements, parenchyma, and fibers.
13. Name the two types of tracheary elements and cite how they differ structurally.
a) Tracheids, which are imperforate, meaning that water and mineral nutrients flow between adjacent cells through the primary cell walls at pit-pairs, which are adjacent holes in the lignified secondary cell wall.
b) Vessel members, which are perforate, meaning that there are one or more continuous holes or perforations, with no intervening primary or secondary cell wall between adjacent cells through which water and minerals may pass.
14. In what taxa are vessels found?
A few species of Equisetum, a few leptosporangiate ferns, all Gnetales (Chapter 5), and almost all angiosperms.
15. What is the function and structure of sieve elements?
Sieve elements are specialized cells that function in the conduction of sugars.
Sieve elements are elongate cells having only a primary cell wall with no lignified secondary cell wall. This primary wall has specialized pores, which are aggregated together into sieve areas.
16. What is phloem?
A tissue composed of sieve elements, parenchyma, and fibers.
17. What is a sieve area and what compound is associated with them?
A region of the primary cell wall with an aggregation of pores, continuous holes in the primary cell wall that are lined with callose, a polysaccharide composed of β-1,3-glucose units.
18. What is the difference, in morphology and taxonomic group where found, between a sieve cell and a sieve tube member?
Sieve cells have only sieve areas on both end and side walls. Sieve tube members have both sieve areas and sieve plates, which consist of one or more sieve areas at the end wall junction of two sieve tube members with significantly larger pores.
19. What is the endodermis and Casparian strip, and what is the function of each?
The endodermis is a specialized cylinder of cells, each cell of which possesses a Casparian strip.
The Casparian strip is a band or ring of lignin and suberin (chemically similar to lignin) that infiltrates the cell wall, oriented tangentially (along the two transverse walls) and axially (vertically, along the two radial walls) and functions as a water-impermeable material that binds to the plasma membrane of the endodermal cells, differentially controlling the solutes that can enter the root vascular system.
20. What is the function of roots?
Roots function in anchorage and absorption of water and minerals.
21. What is the name of the region of actively dividing cells in the root?
Root apical meristem.
22. Name five diagnostic features of roots and their function, if known.
a) The apical meristem is covered on the outside by a rootcap, which functions both to protect the root apical meristem from mechanical damage and to provide lubrication as the outer cells slough off.
b) With the exception of the Psilotopsida (Psilotales and Ophioglossales), the epidermal cells away from the root tip develop hairlike extensions called root hairs, which function to greatly increase the surface area available for water and mineral absorption.
c) Roots have a central vascular cylinder.
d) The vascular cylinder of roots is surrounded by an endodermis with Casparian strips, which function to selectively control which chemicals are and are not absorbed by the plant, functioning in selective absorption. (An undifferentiated layer internal to the endodermis, called the pericycle, is also typically present.)
e) Roots generally have endogenous lateral roots, in which new lateral roots originate by means of actively growing meristems, arising at the pericycle or endodermis.
23. What are mycorrhizae and what is their function in vascular plants?
A symbiotic interaction with various species of fungi. The fungal component of mycorrhizae aids the plant in both increasing overall surface area for water and mineral absorption and increasing the efficiency of selective mineral absorption. The fungus benefits in obtaining photosynthates (sugars and other nutrients) from the plant.
VASCULAR PLANT DIVERSITY
24. What are the characteristics of the rhyniophytes in terms of sporophyte morphology and stem anatomy?
Rhyniophyte sporophytes consisted of dichotomously branching axes bearing terminal sporangia that dehisced longitudinally.
LYCOPODIOPHYTA - LYCOPHYTES
25. Name and give the features of a (paraphyletic) fossil group that diverged along the immediate lineage to the lycophytes.
Zosterophyllophytes, which had no leaves, but possessed lateral sporangia, similar to those of the lycophytes.
26. Name a fossil lycophyte that was a large tree in the Carboniferous and now makes up a large percentage of coal deposits.
27. What are the major apomorphies of the lycophytes?
a) Roots of lycophytes are dichopodial, meaning that the root apical meristem may branch into two roots); no lateral roots develop, as they do in euphyllophytes (see later discussion).
b) Lycophyte roots usually have an endarch protoxylem.
c) Stems of lycophytes have an exarch protoxylem (just the reverse of the roots).
d) Lycophytes, at least ancestrally, have sporangia that are dosiventral (i.e., flattened and having a dorsal, upper, and ventral, lower, surface) and dehisce transversely relative to the axis of the stem or subtending leaf.
e) Lycophytes have sporophytic leaves, which constituted a major adaptive innovation by greatly increasing the area available for light capture in photosynthesis.
28. What are the features of a lycophyll (microphyll)? An enation?
Lycophyll - have a single, unbranched (very rarely branched) vein, lacking a gap in the vasculature of the stem, and develop by an intercalary meristem, i.e., at the base of the leaf.
Enation - external, peg-like appendages that lack vascular tissue.
29. How are lycophylls thought to have evolved?
Lycophylls may have evolved via the development of vasculature tissue leading from the stem into the enation, allowing for more efficient transfer of water and solutes; this was associated with flattening (“planation”) of the enation into a dorsiventral, planar posture. Alternatively, lycophylls may have evolved by the sterilization and planation of sporangia.
30. What is homospory? Name the group and family of lycophytes that have this condition.
Homospory - the condition of having one type of spore, found in the Lycopodiopsida [Lycopodiales], Lycopodiaceae.
31. What is a sporophyll? A strobilus?
Sporophyll - a specialized leaf that bears one or more sporangia.
Strobilus - a cone, consisting of an axis laterally bearing sporophylls.
32. Name three diagnostic features of the Lycopodiaceae.
The Lycopodiaceae are distinctive in being homosporous, dichotomously branched, erect, prostrate, or pendulous, perennial, lycophyllous herbs, the leaves eligulate, the sporangia reniform and transversely dehiscing, born on sporophylls that are photosynthetic and resemble vegetative leaves or that are nonphotosynthetic and scale-like in terminal strobili, the gametophytes mycorrhizal, photosynthetic or saprophytic.
33. What is a ligule?
Ligules are tiny appendages on the upper (adaxial) side of the leaf (both vegetative and reproductive), near the leaf base in the Isoetopsida [Isoetales].
34. Define: endospory, heterospory, megasporangium, megaspore, microsporangium, microspore.
Endospory - the development of gametophytes develop entirely within the original spore wall.
Heterospory - the production of two types of spores, microspores and megaspores.
Megasporangium - the specialized sporangium that produces megaspores.
Megaspore - relatively large spores produced in small numbers within a megasporangium.
Microsporangium - the specialized sporangium that produces microspores.
Microspore - relatively small spores produced in large numbers within a microsporangium.
35. Draw the life cycle of a heterosporous land plant, listing all structures, ploidy levels, and processes.
36. What group and two included families of lycophytes have ligulate leaves and heterospory?
Isoetopsida [Isoetales] - Isoetaceae and Selaginellaceae.
37. Describe the basic morphology of members of the Isoetaceae.
The Isoetaceae are distinctive in being cormose to rhizomatous plants with a basal rosette of microphyllous, ligulate leaves, the leaves basally sheathing, apically linear to acicular, heterosporous, bearing adaxial megasporangia or microsporangia within sheathing leaf base.
38. Name and define the two types of leaf morphology in Selaginella species.
Either homomorphic or dimorphic and four-rowed (with two upper rows of leaves smaller than the two lower rows).
EUPHYLLOPHYTA - EUPHYLLOPHYTES
39. Name the apomorphies of the euphyllophytes, and list the two major, vascular plant groups included.
a) Roots are monopodial.
b) Roots have an exarch protoxylem.
c) The ancestral sporangia were terminal in position with longitudinal deshiscence.
d) Extant euphyllophytes have a 30-kilobase inversion located in
the large single-copy region of chloroplast DNA.
e) Leaves of euphyllophytes, termed euphylls, are distinctive.
Two major groups:
Monilophytes and Lignophytes/Spermatophytes.
40. How do euphylls differ from lycophylls?
Euphylls are different in being associated with a leaf gap, a region of nonvascular, parenchyma tissue interrupting the vasculature of the stem, and in (usually) having more than one vein per leaf. Euphylls, in contrast to lycophylls, grow by means of either marginal or apical meristems.
41. What (paraphyletic) fossil group diverged along the immediate lineage to euphyllophytes?
42. Describe a widely accepted hypothesis regarding the evolution of the euphyll.
By one hypothesis, euphylls evolved via the transformation of 3-dimensional (nonplanar) lateral branch system (as seen in trimerophytes) into a leaf, by the processes of planation, flattening of the axes into a 2-dimensional plane, and webbing, the development of thin tissue between the axes of the branches (Figure 4.20E). The original axes become transformed into veins, and the “web” functioned as a photosynthetic mesophyll.
43. What is a shoot?
A stem plus associated leaves.
44. What is the name of the region of actively dividing cells in a shoot, and how does this differ among vascular plants?
a) Shoot apical meristem;
b) The apical meristem may contain one, dominant apical cell, found in most of the Selaginellaceae and the monilophytes, or a complex of several, actively dividing cells, found in the Lycopodiaceae, Isoetaceae, and the euphyllophytes.
45. Define node; internode.
The region between two adjacent nodes.
46. What is the general morphology and function of leaves?
Leaves are usually dorsiventral organs (with some exceptions), both an upper and lower epidermis can be defined. As with all land plants, a cuticle covers the outer cell wall of the epidermal cells. One or more vascular bundles, or veins, contain xylem and phloem tissue and conduct water and sugars to and from the chloroplast-containing mesophyll cells. The mesophyll of some leaves is specialized into upper, columnar palisade mesophyll cells and lower, irregularly shaped spongy mesophyll cells, the latter with large intercellular spaces. Stomata, which function in gas exchange are found typically only in the lower epidermis of leaves.
Leaves are the primary photosynthetic organ of plants.
47. What is a vein?
A vascular bundle that contains xylem and phloem tissue and conducts water and sugars to and from the chloroplast-containing mesophyll cells.
48. What are the internal, chlorophyllous cells of a leaf called? Into which two layers may these cells be organized?
b) Upper, columnar palisade mesophyll cells and lower, irregularly shaped spongy mesophyll cells, the latter with large intercellular spaces.
49. What is the definition of a bud and where are they typically located?
Bud = an immature shoot system.
They are typically located in the axils of leaves.
50. What is monopodial growth?
A growth in which the terminal apical meristem continues and in which lateral branches develop from axillary buds.
MONILOPHYTA - MONILOPHYTES
51. Name the putative apomorphies of the monilophytes, and list the five major groups contained within it.
Apomorphies: a) Siphonostele; b) Stem protoxylem is mesarch in position.
Groups: Equisetopsida; Polypodiopsida; Marattiopsida; Psilotopsida (including Psilotales and Ophioglossales).
52. What is a siphonostele? Name the types of siphonosteles.
A siphonostele is a type of stem vasculature in which a ring of xylem is surrounded by an outer layer of phloem (ectophloic siphonostele) or by an outer and inner layer of phloem (amphiphloic siphonostelesolenostele; if dissected called a dictyostele).
EQUISETOPSIDA - EQUISETOPHYTES
53. What fossil member of the equisetophytes makes up a component of coal deposits?
54. Name the major apomorphies of the equisetophytes.
1) Ridged stems; 2) reduced, whorled leaves that are usually marginally fused; 3) sporangiophores, each of which consists of a peltate axis bearing pendant longitudinally dehiscent sporangia; and 4) photosynthetic spores with elaters.
55. What is the only extant genus and family of this group?
56. What do equisetophytes have as a component of the cell wall?
57. What is the difference between a scouring rush and a horsetail? Into what two subgenera are these classified?
Scouring rushes (subgenus Hippochaete) lack (or have very few) whorls of lateral branches and have sunken stomates.
Horsetails (subgenus Equisetum) have numerous, whorled, lateral branches and stomates flush with the epidermis.
58. Describe the morphology of the strobilus (cone), sporangiophore, and sporangia of Equisetum.
Sporangia are homosporous, born in terminal strobili (subtended by a whorl of sheathing leaves), consisting of an axis bearing numerous, peltate sporangiophores, each (at maturity) bearing 5–10 sporangia beneath the distal, hexagonal outer portion; dehiscence is longitudinal (parallel to the axis of the elongate sporangium).
59. What is unique about the spores of Equisetum? What is the function of this novelty?
Spores, which lack an attachment scar, are spherical, green (with chloroplasts), each bearing four,
spatulate, hygroscopic elaters (derived from the spore wall), which coil and uncoil with changes in humidity, functioning in spore dispersal.
PSILOTOPSIDA - PSILOTOPHYTES
60. What features about the roots and gametophytes are presumed apomorphies for the Psilotopsida?
The roots of Ophioglossales are unusual in lacking both root branches and root hairs, and those of the Psilotales are lacking. The gametophytes of both orders are nonphotosynthetic (heterotrophic), contain mycorrhizal fungi, and are often subterranean.
61. What is a eusporangium?
A sporangium that is relatively large, is derived from several epidermal cells, has a sporangial wall comprised of more than one cell layer, and produces very many (usually thousands of) spores
62. What is distinctive about the leaves of the Ophioglossales/Ophioglossaceae, the ophioglossoid ferns?
The ophioglossoid ferns are unique in that each leaf (or “frond”) consists of a sterile segment, which contains the photosynthetic blade or lamina, and a fertile segment, bearing the sporangia.
63. What is a synangium?
A fusion product of sporangia.
64. What is distinctive (and apomorphic) about the roots, leaves, and sporangia of the Psilotaceae, the whisk ferns?
Roots are absent. Leaves are reduced to microphylls or enations. Sporangia are fused (synangia).
65. What are the two genera of the Psilotaceae? What species is a commonly cultivated ornamental?
Psilotum and Tmesipteris. Psilotum nudum is a common cultivar.
MARATTIOPSIDA - MARATTIOID FERNS
66. Name and describe the diagnostic features and a putative apomorphy of the marattioid ferns.
The Marattiaceae are distinctive in being large, terrestrial ferns with mucilage canals, the stems with a polycyclic dictyostele, the leaves generally large, simple to several-pinnate, with abaxial, intramarginal eusporangia, sometimes fused into synangia.
67. How do the gametophytes, leaf type, and leaf development of the marattioid ferns resemble the leptosporangiate ferns?
Gametophytes are photosynthetic. Leaves are simple to many-compound with abaxial sporangia. Leaf development is by means of circinate vernation.
68. What type of sporangium is found in the marattioid ferns?
POLYPODIOPSIDA - LEPTOSPORANGIATE FERNS
69. Name three stem types/habits that occur in the leptosporangiate ferns.
Rhizome, arborescent, and vine stem.
70. What is circinate vernation? What terms are used for immature fern leaves that exhibit this?
a) Development in which immature parts are coiled. b) Crozier or “fiddlehead.”
71. Define frond, stipe, pinna, pinnule.
Frond - term for a fern leaf. Stipe - term for a fern petiole. Pinna - term for first discrete leaflets or leaf divisions of a fern leaf. Pinnule - term for the ultimate leaftlet or leaf division of a fern leaf.
72. What aspects of venation and scale morphology are useful in leptosporangiate fern classification?
Venation - whether pinnate, palmate, open/free (simple, forked, or bifurcate), or reticulate/anastamosing.
Scale morphology - whether clathrate or non-clathrate.
73. What is the major apomorphy of the Polypodiopsida? Describe its development and morphology.
The leptosporangium, a sporangium that develops from a single epidermal cell, has a single cell layer of the wall at maturity, and produces a relatively small number of spores.
74. Define annulus, sorus, indusium, false indusium, acrostichoid.
Annulus - a single row of cells of the leptosporangium in which the cell walls are differentially thickened on the inner cell face and on the faces between adjacent annular cells.
Sorus - a cluster of leptosporangia.
Indusium - a flap-like structure that may cover the sorus.
False indusium - a flap-like structure that covers a sorus or group of leptosproangia that arises from the margin of a leaf or leaflet.
Acrostichoid - a morphology in which numerous leptosporangia cover an extensive area of the blade, and are not arranged into discrete sori.
75. Name aspects of sorus morphology, indusium morphology, sporangium development, sporangium morphology, and spore type used in fern classification.
Sorus morphology - shape (in outline), variation in the shape and size of the receptacle, and presence and morphology of paraphyses.
Indusium morphology - present (indusiate) or absent (exindusiate), shape (e.g., reniform, orbicular, linear), and attachment point (e.g., peltate or lateral).
Sporangium development - sequence of development, whether gradate (acropetalous, basipetalous), simultaneous, mixed, or intermingled.
Sporangium morphology - length and number of stalk cells, body size and shape, and morphology and position of the annulus (e.g., whether lateral, transverse, apical, oblique), stomium, and dehiscence line
Spore type - whether trilete, monolete, or alete.
76. In a fern gametophyte, what is the name of the male gametangium? The female gametangium? What do they look like?
a) Antheridium - usually spheric; b) archegonium - with a protruding neck.
77. What is unique about the leaf morphology and sporangium annulus of the Osmundaceae?
Leaves are dimorphic with either fertile and sterile leaves or with fertile and sterile leaf segments.
Sporangium annulus is lateral in position.
78. What is the common name of the Hymenophyllaceae? What is unique about its indusium, receptacle, and leaf anatomy?
a) Filmy fern family.
b) Indusium is conical, tubular, or 2-lobed; receptacle is elongate; leaves usually consist of a single layer of cells.
79. Describe the leaf morphology of the Gleicheniaceae.
Leaves are usually long, indeterminate, pseudodichotomously branched.
80. What is unique about the leaf morphology, sorus, indusium, and sporangium annulus of the Lygodiaceae?
Leaf morphology - Leaves are indeterminate, with twining/climbing rachises, alternately bearing pseudodichotomously-branching pinnae, leaf segments dimorphic.
Sorus - at the tips of ultimate segments, each with only one sporangium.
Indusium - flap or flange-like.
Annulus - transverse, subapical, continuous.
81. What is distinctive and apomorphic about the life cycle of the Salviniales? What is a sporocarp and what is its function?
a) They are heterosporous.
b) The sporocarp is a seed-like protective and dormant reproductive propagule. The sporocarp “germinates,” releasing endosporic megaspores and microspores.
82. Name the two families of the Salviniales and describe how they differ. Name two genera in each family.
Marsileaceae (Marsilea, Pilularia, Regnellidium) - have emergent leaves with 4, 0, or 2 leaflets, respectively.
Salviniaceae (Azolla, Salvinia) - have floating leaves.
83. How is Azolla of great economic importance?
It houses a symbiotic blue-green bacterium, Anabaena azollae, which fixes nitrogen. When “seeded” in rice paddies, Azolla’s symbiotic relationship results in an enhancement of nitrogen content in the surrounding water, enabling rice plants to grow more vigorously.
84. What is distinctive about the sorus and indusium of the Aspleniaceae?
They are linear.
85. Name a diagnostic feature of the sorus and indusium of the Dryopteridaceae, Polypodiaceae, and Pteridaceae.
Dryopteridaceae - Sori are usually round, indusiate or exindusiate, acrostichoid in some taxa. Indusia, when present, are round-reniform or peltate.
Polypodiaceae - Sori are abaxial (rarely marginal), round, oblong, or elliptic, rarely elongate or acrostichoid, the receptacle often with paraphyses, exindusiate.
Pteridaceae - Sori are exindusiate, either marginal with a false indusium formed by a reflexed marginal flap or intramarginal in lines along veins, the receptacle generally not raised.