Difficulty: Intermediate | Prerequisites: Part 1 (Plant Diversity Fundamentals)
This is the second part of the B130 Plant Diversity lab notes. It covers the 14 character traits used to compare seven plant groups (green algae, liverworts, mosses, lycophytes, ferns, gymnosperms, angiosperms) and the completed character matrix. You need to understand alternation of generations and basic plant anatomy from Part 1 before this will click.
The lab uses 14 character traits to compare seven plant groups. Traits 1 to 5 cover physical structure (cuticle, gas exchange, vascular tissue, leaf type, height). Traits 6 to 14 cover reproduction and life cycle (pollen, dominant life stage, independence of gametophyte and sporophyte, embryo care, sperm delivery, spore care, heterospory, and seeds). The resulting character matrix is the raw data for building a phylogenetic tree.
Character matrix
A table that records the state of each trait for every organism being compared. Each row is a plant group, each column is a trait, and each cell holds a numerical code for the observed state. This matrix feeds into phylogenetic software (Mesquite, in this lab) to generate the most parsimonious tree.
Outgroup
A taxon known or assumed to be outside the group of interest. In this lab, green algae serve as the outgroup, helping to root the phylogenetic tree and determine which traits are ancestral versus derived.
Parsimony
The principle that the simplest explanation (fewest evolutionary changes) is preferred when building a phylogenetic tree. Mesquite uses a heuristic parsimony search to find the tree requiring the fewest character-state changes.
Synapomorphy
A shared derived character that is evidence of common ancestry. For example, seeds are a synapomorphy uniting gymnosperms and angiosperms.
Convergent evolution
When similar traits evolve independently in unrelated lineages due to similar selective pressures, rather than being inherited from a common ancestor. Heterospory likely evolved convergently in multiple plant lineages.
1. Cuticle (0 = absent, 1 = present)
A waxy waterproof layer on exposed plant surfaces. All land plants have a cuticle. Algae do not. Test: water beads up on a cuticle, spreads or absorbs without one.
2. Regulation of gas exchange (0 = none, 1 = pores, 2 = pores with guard cells)
Algae have no pores (gas diffuses directly through wet surfaces). Liverworts have pores but no guard cells, so they cannot regulate opening. All other land plant groups have stomata: pores flanked by guard cells that open and close.
3. Vascular tissue (lignin) (0 = absent, 1 = present)
Present in lycophytes, ferns, gymnosperms, and angiosperms. Absent in green algae, liverworts, and mosses. Composed of xylem (lignified, carries water/minerals) and phloem (no lignin, carries sugars). Under a microscope, xylem cells appear large, empty, with thin red-stained walls; phloem cells are smaller with green or blue-stained walls.
4. Leaf type (0 = microphyll, 1 = macrophyll)
Applies only to vascular plants (non-vascular plants lack true leaves). Lycophytes have microphylls (one vein per leaf). Ferns, gymnosperms, and angiosperms have macrophylls (multiple veins).
5. Maximum erect height greater than 5 cm (0 = absent, 1 = present)
Lignin and vascular tissue enable structural support for upright growth. Ferns, lycophytes, gymnosperms, and angiosperms can exceed 5 cm. Algae, liverworts, and mosses cannot (or remain close to the ground).
6. Pollen (reduced male gametophyte) (0 = absent, 1 = present)
Present in gymnosperms and angiosperms only. Pollen is a male gametophyte reduced to just two cells, small enough to be wind- or animal-dispersed.
7. Largest life stage (0 = gametophyte, 1 = sporophyte)
In algae, liverworts, and mosses, the gametophyte is the dominant, larger stage. In lycophytes, ferns, gymnosperms, and angiosperms, the sporophyte dominates.
8. Independent gametophyte (0 = absent, 1 = present)
A gametophyte is independent if it is photosynthetic and physically detached from the sporophyte at some point. Present in algae, liverworts, mosses, lycophytes, and ferns. Absent in gymnosperms and angiosperms (their gametophytes are tiny and retained within the sporophyte).
9. Independent sporophyte (0 = absent, 1 = present)
A sporophyte is independent if it is photosynthetic and detached from the gametophyte at some point. Present in all groups except liverworts and mosses, where the sporophyte remains attached to the gametophyte.
10. Care of sporophyte embryo (0 = develops outside parent, 1 = develops inside parent)
In algae, the zygote develops in open water. In all land plant groups, the embryo develops inside the parent plant's tissues, receiving protection and nourishment.
11. Type of sperm (0 = free-swimming, 1 = delivered in pollen tube)
Free-swimming in algae, liverworts, mosses, lycophytes, and ferns (requires standing water). Delivered via pollen tube in gymnosperms and angiosperms.
12. Care of spores (0 = released to environment, 1 = retained by sporophyte)
Released to the air in algae, liverworts, mosses, lycophytes, and ferns. Retained within the sporophyte in gymnosperms and angiosperms (spores develop into gametophytes inside the parent plant).
13. Heterospory (0 = absent, 1 = sometimes present, 2 = always present)
Absent in algae, liverworts, and mosses (all spores the same size). Sometimes present in lycophytes and ferns (varies by species). Always present in gymnosperms and angiosperms (microspores and megaspores).
14. Seeds (0 = absent, 1 = present)
Present only in gymnosperms and angiosperms. A seed packages the embryo with nutritive tissue and a protective coat, allowing survival and dispersal without standing water.
Trait | Green Algae | Liverwort | Moss | Lycophyte | Fern | Gymnosperm | Angiosperm |
|---|---|---|---|---|---|---|---|
1. Cuticle | 0 | 1 | 1 | 1 | 1 | 1 | 1 |
2. Gas exchange | 0 | 1 | 2 | 2 | 2 | 2 | 2 |
3. Vascular tissue | 0 | 0 | 0 | 1 | 1 | 1 | 1 |
4. Leaf type | n/a | n/a | n/a | 0 (micro) | 1 (macro) | 1 (macro) | 1 (macro) |
5. Height >5 cm | 0 | 0 | 0 | 1 | 1 | 1 | 1 |
6. Pollen | 0 | 0 | 0 | 0 | 0 | 1 | 1 |
7. Largest stage | 0 (gam.) | 0 (gam.) | 0 (gam.) | 1 (spor.) | 1 (spor.) | 1 (spor.) | 1 (spor.) |
8. Indep. gametophyte | 1 | 1 | 1 | 1 | 1 | 0 | 0 |
9. Indep. sporophyte | 1 | 0 | 0 | 1 | 1 | 1 | 1 |
10. Embryo care | 0 | 1 | 1 | 1 | 1 | 1 | 1 |
11. Sperm type | 0 | 0 | 0 | 0 | 0 | 1 | 1 |
12. Spore care | 0 | 0 | 0 | 0 | 0 | 1 | 1 |
13. Heterospory | 0 | 0 | 0 | 1 | 1 | 2 | 2 |
14. Seeds | 0 | 0 | 0 | 0 | 0 | 1 | 1 |
Students often think "leaf type" applies to all plants. It does not. Only vascular plants have true leaves. Non-vascular plants (algae, liverworts, mosses) have leaf-like structures but these are not coded for leaf type in the matrix.
Students sometimes assume that because mosses look green and leafy, they must have vascular tissue. Mosses are non-vascular. Their small size is a direct consequence of lacking internal transport.
Students confuse "independent" gametophyte/sporophyte with "dominant." Independent means photosynthetic and physically detached at some point. A stage can be independent but small (like the fern gametophyte), or dependent but large (like the moss sporophyte, which is attached to and nutritionally reliant on the gametophyte).
Students sometimes think heterospory and seeds are the same adaptation. Heterospory (producing two sizes of spore) is a prerequisite for seeds, but heterosporous plants such as certain lycophytes and ferns do not produce seeds.
True or false: Liverworts have stomata (pores with guard cells). False. Liverworts have pores but no guard cells.
Fill in the blank: The only plant groups that produce pollen are ___ and ___. Gymnosperms and angiosperms.
True or false: Ferns produce seeds. False. Ferns are seedless vascular plants.
Fill in the blank: Heterospory is the production of two different sizes of spore called ___ and ___. Microspores and megaspores.
True or false: In mosses, the sporophyte is the dominant life stage. False. The gametophyte is dominant in mosses.
Q: Which plant groups lack vascular tissue? What does this mean for their body size?
A: Green algae, liverworts, and mosses lack vascular tissue. Without internal transport, every cell must be near a water and nutrient source, which limits body size.
Q: Looking at the character matrix, which traits are shared by gymnosperms and angiosperms but absent in all other groups?
A: Pollen (trait 6), sperm in pollen tubes (trait 11), spores retained by the sporophyte (trait 12), heterospory always present (trait 13 = 2), and seeds (trait 14). These are synapomorphies of seed plants.
Q: What is the difference between a microphyll and a macrophyll? Which plant group has microphylls?
A: A microphyll is a small leaf with a single vein. A macrophyll is a larger leaf with multiple veins. Lycophytes have microphylls; ferns, gymnosperms, and angiosperms have macrophylls.
Q: Why is heterospory considered a case of convergent evolution in plant phylogeny?
A: Heterospory appears in some lycophytes, some ferns, and all seed plants. Because these groups are not all each other's closest relatives, heterospory likely evolved independently multiple times rather than being inherited from a single common ancestor.
Q: Explain the difference between "care of spores" and "care of sporophyte embryo."
A: Care of spores (trait 12) refers to whether the sporophyte releases its spores to the environment or retains them internally (where they develop into gametophytes in situ). Care of sporophyte embryo (trait 10) refers to whether the zygote/embryo develops inside the parent plant's tissues (protected) or outside in the environment.
⚠️ The character matrix is the foundation of the phylogenetic tree. Expect exam questions asking you to read the matrix and identify which groups share derived traits.
⚠️ Be able to distinguish homology (shared ancestry) from convergence (independent evolution). Heterospory is the classic convergent example from this lab.
⚠️ Know the progression of adaptations from algae to angiosperms: cuticle and embryo care first (land plants), then vascular tissue (lycophytes onward), then pollen, seeds, and retained spores (seed plants). This sequence maps directly onto the phylogenetic tree.
The character matrix feeds directly into the phylogenetic tree construction covered in Part 3 of these notes. The reproductive traits (6 to 14) connect to the Plant Reproduction lab, where life cycles of mosses, ferns, gymnosperms, and angiosperms are examined in detail. Understanding which traits are convergent versus synapomorphic is core material for any evolution or systematics exam.
Character matrix, character traits, B130, BIOL 130, plant diversity lab, cuticle, gas exchange, stomata, guard cells, pores, vascular tissue, xylem, phloem, lignin, microphyll, macrophyll, leaf type, erect height, pollen, gametophyte, sporophyte, independent gametophyte, independent sporophyte, embryo care, free-swimming sperm, pollen tube, spore care, heterospory, homospory, microspore, megaspore, seeds, seed plants, character coding, Mesquite, parsimony, synapomorphy, convergent evolution, outgroup, green algae, liverwort, moss, lycophyte, fern, gymnosperm, angiosperm