Evolutionary History of Land Plants - Comparative Morphology

Lab 10: Evolutionary History of Land Plants - Comparative Morphology

Objectives

By the end of this lab, you'll understand:

• The diversity of seedless plants (mosses, liverworts, ferns, and fern allies)

• Key evolutionary adaptations for life on land

• How plant structure relates to habitat requirements

• The shift from gametophyte-dominated to sporophyte-dominated life cycles

• Why some plants still need water for reproduction

• How desert environments limit non-vascular plant distribution

Background

Plants originated in water ~470 million years ago. Moving onto land required major evolutionary innovations!

Challenges of terrestrial life:

1. Desiccation - Air dries out tissues

2. Structural support - No water buoyancy

3. Reproduction - No water to carry sperm to eggs

4. Nutrient/water transport - No diffusion from surrounding water

5. UV radiation - More intense than underwater

Evolutionary solutions:

EVOLUTIONARY BACKGROUND

Bryophytes (Mosses & Liverworts)

The "pioneers" of land plants - simplest and oldest

Key characteristics:

• No vascular tissue (no xylem or phloem = no veins!)

• No true roots, stems, or leaves (these terms reserved for vascular plants)

• Gametophyte dominant - The green leafy stage you see is the gamete-producing generation

• Sporophyte dependent - The stalk with capsule grows ON and gets nutrition FROM the gametophyte

• Need water for reproduction - Sperm must swim to eggs

• Stay small (usually <10 cm tall)

Why they're limited:

• No vascular tissue = can't move water far

• No roots = can't tap deep water

• Must absorb water through leaves = need humid environments

• Small size = prone to drying out

Pteridophytes (Ferns & Fern Allies)

More advanced - appeared ~420 million years ago

Key characteristics:

• Have vascular tissue (xylem & phloem = veins!)

• Have true roots, stems, and leaves (defined by vascular tissue)

• Sporophyte dominant - The leafy plant you see produces spores

• Gametophyte independent but tiny - Heart-shaped, ~5mm, on soil surface

• Still need water for reproduction - Sperm swim on gametophyte

• Can grow much larger (some ferns >2 meters tall)

Why they're more successful:

• Vascular tissue = can transport water efficiently

• Roots = can access deep water

• Larger size = compete better for light

• Still limited to moist environments for reproduction

Where to Find Seedless Plants in Mohave County:

Bryophytes (very limited):

• Along Colorado River, Lake Havasu, Lake Mohave (if accessible)

• North-facing rock crevices with seeps

• Irrigated areas (parks, gardens) - look on pavement edges, fountain bases

• Higher elevations (Hualapai Mountains if accessible)

Pteridophytes (slightly more common):

• Riparian corridors along perennial streams

• Canyon bottoms with permanent water

• Landscape plantings (gardens, parks)

Alternatives if no natural sites available:

• Visit botanical nursery

• Use preserved specimens from Mohave College herbarium

Materials

Equipment:

• Measuring tape

• Resealable plastic bags

• Water bottle

• Camera

• Trowel

• Scale

• Plant identification apps

Study Sites:

Required access to moist habitats (challenging in Arizona!):

Option 1: Natural sites (if available):

• Permanent springs

• Perennial stream banks

• North-facing canyon walls with seeps

• Riparian corridors

Option 2: Anthropogenic sites (more reliable):

• Irrigated parks with shaded areas

• Fountain bases and drainage areas

• Nurseries (with permission)

• Use indoor ferns from homes/offices

Part 1: Bryophyte Survey - Mosses & Liverworts

Goal: Document the simplest land plants and understand their limitations.

Mosses look like miniature forests:

• Tiny "leaves" arranged on "stems" (technically not true leaves/stems)

• Often form cushions or mats

• May have stalks with capsules (sporophytes)

• Grow on almost any surface

• Typically bright to dark green when moist

Liverworts look flatter:

• Thalloid types: Ribbon-like, flat, no obvious leaves (look like green seaweed)

• Leafy types: Look like flattened mosses

• May have umbrella-like reproductive structures

• Often smell earthy or spicy when crushed

• Usually darker green or purple-tinged

Step 1: Find Moss Collection Sites

Natural sites (rare):

• North sides of boulders near water sources

• Shaded canyon walls with seepage

• Edges of permanent springs

• Riparian zones along Colorado River

• Higher elevation mountains (Hualapai, if accessible)

Urban/modified sites (more successful):

• Irrigation channels and overspray areas

• Shaded pavement cracks near sprinklers

• Fountain bases (constantly wet)

• North-facing walls of air-conditioned buildings (condensation)

• Under outdoor faucets with slow drips

• Nursery greenhouse floors

Goal: Find at least 3-5 different-looking moss types

• Don't worry about exact species names

• Just find obvious differences in:

  • Growth form (cushion vs. mat vs. trailing)

  • Color (bright green vs. dark green vs. yellow-green)

  • Leaf shape (wide vs. narrow)

  • Size (tiny vs. relatively large)

Step 2: Document Each Moss Type

For each moss collection:

A. Take In Situ Photo

What to include:

• Overview showing location and context

• Close-up showing growth pattern

• Scale reference (ruler)

• Substrate (what it's growing on)

Photo tips:

• Get down to moss level

• Use macro mode if available

• Ensure good lighting

B. Measure Colony

Colony = the patch of moss growing together

Measurements:

• Diameter: Widest dimension across patch (cm)

• Depth/Height: How thick is the mat? (mm or cm)

• Coverage: What % of available substrate covered?

Recording:

• Colony diameter: _____ cm

• Colony depth: _____ mm

• Percent coverage: _____%

C. Describe Growth Form

Check which best describes the colony:

• Cushion: Rounded, dome-like clump (like a pin cushion)

  • Typical height: 1-3 cm

  • Individual stems tightly packed

• Mat (sheet): Flat, carpet-like spread (like a rug)

  • Typical height: <1 cm

  • Covers area horizontally

• Tuft (haircap): Upright clump, not dense (like grass clump)

  • Individual stems visible

  • Space between stems

• Trailing: Long strands, hanging or creeping

  • Found on vertical surfaces or logs

  • Individual stems obvious

Recording: Growth form: _____

D. Note Substrate

What is the moss growing on?

• Soil (type: sand / clay / loam / organic)

• Rock (type: sandstone / granite / limestone / other)

• Tree bark (tree species if known: _____)

• Rotting wood (decay stage: fresh / partly rotted / very rotten)

• Concrete/pavement

• Other: _____ (brick, metal, etc.)

Recording: Substrate: _____

E. Assess Moisture

Current moisture level of moss:

• Dry - Crispy, brown or pale, brittle

• Moist - Green, soft, flexible

• Wet - Dripping, saturated, water visible

• Submerged - Actually in water

Also note:

• Source of moisture: Rain  /  Irrigation  /  Seepage  /  Condensation  /  Stream

• Frequency of moisture: Constant  /  Daily  /  Weekly  /  Occasional

Recording: Moisture level: _____

F. Look for Sporophytes

Sporophytes = the reproductive stalks sticking up from moss

What they look like:

• Thin stalk (seta) rising from moss leaves

• Capsule (spore container) at top

• May have cap (calyptra) on capsule

• Color: Usually brown when mature, green when young

Record:

• Present or Absent? Present  /  Absent

• If present:

  • Count how many: _____ (or estimate if numerous)

  • Height from moss surface to top of capsule: _____ mm

  • Capsule color: Green  /  Brown  /  Red  /  Yellow  /  Black

  • Capsule shape: Cylindrical  /  Egg-shaped  /  Urn-shaped  /  Spherical

  • Maturity: Immature (green, cap intact)  /  Mature (brown, cap may be off)

Sporophytes indicate sexual reproduction occurred—sperm swam to eggs!

G. Collect Small Sample

Collection ethics:

• Only collect from abundant populations

• Take thumbnail-sized piece only

• Leave majority of colony intact

• Don't collect from rare species or protected areas

• In Arizona, be especially conservative (mosses are rare!)

Procedure:

1. Carefully pinch or cut small piece

2. Include several individual "stems" with leaves

3. Try to include base with rhizoids if possible

4. Place on white paper or in labeled bag

5. Keep moist during transport (spray with water)

Labeling:

• Collection number: M1, M2, M3... (M = moss)

• Location: _____

• Date and time: _____

• Substrate: _____

• Collector initials: _____

Step 3: Detailed Microscopic Observations

Back at your work area, examine samples with hand lens or camera zoom:

Setup:

• Place moss on white paper or card

• Use good lighting (desk lamp ideal)

• Spray lightly with water (helps see details)

• Separate individual stems for examination

For Each Moss Type:

A. Leaf Arrangement on Stem

How are leaves attached?

• Spiral - Leaves wrap around stem in spiral pattern (most common)

• Opposite - Leaves in pairs directly across from each other

• Whorled - Leaves in circles around stem at nodes

• Two-ranked - Leaves in two rows on opposite sides

Recording: Leaf arrangement: _____

B. Leaf Shape

Look closely with hand lens!

Common shapes:

• Oval/Ovate - Egg-shaped

• Lance-shaped/Lanceolate - Long and pointed like spearhead

• Triangular - Three-sided

• Rounded - Circular

• Linear - Very narrow and long

• Spatulate - Spoon-shaped

Additional features:

• Apex (tip): Pointed  /  Rounded  /  Notched

• Base: Tapered  /  Rounded  /  Heart-shaped

• Margins (edges): Smooth  /  Toothed  /  Wavy

Recording: Leaf shape: _____ Sketch: Draw what you see!

C. Leaf Size

Procedure:

1. Select 3 typical leaves

2. Measure length from base to tip (mm)

3. Calculate average

Measurements:

• Leaf 1: _____ mm

• Leaf 2: _____ mm

• Leaf 3: _____ mm

• Average: _____ mm

Typical range: 0.5-5 mm for most mosses

D. Midrib (Costa)

A thickened line running down center of leaf (looks like a vein, but isn't true vascular tissue)

Check for presence:

• Present - Clear midrib visible

  • Extends to tip or stops partway? _____

  • Single or double (forked)? _____

  • Color: Same as leaf  /  Darker  /  Lighter

• Absent - No midrib visible

Recording: Midrib: Present  /  Absent

E. Stem Characteristics

Color:

• Green (photosynthetic)

• Brown

• Red/reddish

• Black

Branching pattern:

• Unbranched (simple, single stem)

• Sparingly branched (few branches)

• Highly branched (many branches, tree-like)

Stem thickness: _____ mm (if measurable)

Recording: Stem color: _____ Branching: _____

F. Rhizoids

Root-like threads at base of stem (absorb water, anchor plant)

NOT true roots! (No vascular tissue)

Observations:

• Visible without magnification? Yes  /  No

• Color: Brown  /  Colorless  /  Green

• Abundance: Few  /  Moderate  /  Numerous (dense mat)

• Location: Base only  /  Along entire stem

Recording: Rhizoids: _____

G. Capsule Details (If Sporophytes Present)

Capsule = spore container at top of stalk

Shape:

• Cylindrical (like tube)

• Egg-shaped (ovoid)

• Urn-shaped (like vase)

• Spherical (round)

Calyptra (cap on top):

• Present (covering capsule)

• Fallen off

• Shape if present: Hood-like  /  Conical  /  Mitre-like

Operculum (lid on capsule):

• Present (capsule closed)

• Fallen off (capsule open, releasing spores)

Peristome teeth (at capsule opening):

• Visible when operculum falls off

• Look like tiny teeth around opening

• Control spore release

Recording: Capsule details: _____

Step 4: Search for Liverworts

Liverworts are MUCH RARER than mosses, especially in Arizona!

Where to look (if you're lucky):

• Very wet rocks along permanent streams

• Dripping cliffs or seeps (rare in desert)

• Moist soil in deep shade near water

• Old, rotting logs in riparian areas

• Around hot springs (if accessible)

Arizona reality: You probably won't find liverworts in Mohave County unless visiting specialized habitat. That's okay! Understanding WHY they're absent is educational.

If you DO find liverworts:

Types to look for:

1. Thalloid Liverworts:

• Flat, ribbon-like structures

• Look like green leather or seaweed

• May have hexagonal patterns on surface (air pores)

• Look for umbrella-like structures on stalks (archegoniophores)

2. Leafy Liverworts:

• Similar to mosses but:

  • Usually flatter, more prostrate

  • Leaves often in two rows (not spiral)

  • Leaves may be lobed or divided

  • Often slightly translucent

  • Underleaves present (third row underneath)

Document same measurements as for mosses!

Special structures to find:

• Gemma cups: Cup-like structures with tiny discs (asexual reproduction)

• Antheridiophores: Male structures (look like tiny palm trees or flat discs on stalks)

• Archegoniophores: Female structures (look like tiny umbrellas - rays extending from top of stalk)

Step 5: Data Table for Bryophytes

Part 2: Pteridophyte Survey - Ferns & Fern Allies

Goal: Document vascular seedless plants and understand their advantages over bryophytes.

Ferns:

• Large divided leaves called fronds

• Usually have brown/orange dots on underside (sori = clusters of sporangia)

• Coiled new growth (fiddleheads or crosiers)

• Underground stem (rhizome)

• True roots, stems, and leaves (with vascular tissue!)

Fern Allies (rare, but interesting):

• Horsetails (Equisetum): Jointed, bamboo-like stems with whorls of branches

• Club mosses (Lycopodium, Selaginella): Look like big mosses but have vascular tissue

• Much rarer than true ferns in Arizona

Step 1: Find Fern Collection Sites

Natural sites (limited):

• Permanent stream banks (Colorado River tributaries)

• North-facing canyon walls with constant moisture

• Riparian corridors

Modified sites (more accessible):

• Landscape plantings (parks, businesses, homes)

• Nurseries (can purchase specimens for study)

Cultivated ferns common in Arizona landscapes:

• Maidenhair fern (Adiantum) - Delicate, fan-shaped leaflets

• Autumn fern (Dryopteris) - Coppery new growth

• Holly fern (Cyrtomium) - Glossy, holly-like leaflets

• Sword fern (Nephrolepis) - Common houseplant

• Bracken fern (Pteridium) - If in disturbed moist areas

Goal: Find at least 3-5 different fern species or types

Step 2: Document Each Fern

For each fern collected or observed:

A. Take Photos

Required shots:

1. Whole plant - Overall form and habit

   • Shows how fronds emerge from ground

   • Indicates whether clumping or spreading

2. Close-up of frond - Division pattern clear

   • Shows pinnae arrangement

   • Shows how leaflets attach

3. Underside of frond - Showing sori if present

   • Key for identification!

   • Shows spore-producing structures

4. Fiddlehead (if present) - Coiled emerging frond

   • Beautiful and diagnostic

   • Only visible in growing season

B. Measure Frond Length

What to measure: From base (where attached to rhizome) to tip of longest division

Procedure:

1. Select longest mature frond

2. Straighten (don't damage!)

3. Measure along midrib to tip

4. Record in cm

Recording: Frond length: _____ cm

Typical ranges:

• Small ferns: 10-30 cm

• Medium ferns: 30-80 cm

• Large ferns: 80-200+ cm

C. Count Pinnae

Pinnae = the major divisions along the frond (singular: pinna)

Procedure:

1. Pick a typical, mature frond

2. Count major divisions on ONE side only

3. Don't count the terminal (tip) section

Recording: Number of pinnae: _____

D. Describe Frond Shape/Division

Ferns classified by division level:

Simple (undivided):

• Entire blade, no divisions

• Looks like single leaf

Pinnate (once-divided):

• Frond divided into pinnae

• Looks like feather

Bipinnate (twice-divided):

• Frond divided into pinnae

• More complex, lacy appearance

Tripinnate (three-times divided):

• Pinnae divided into pinnules

• Very lacy, delicate appearance

Recording: Division level: _____

E. Check for Fertile vs. Sterile Fronds

Some ferns have two frond types:

Sterile fronds:

• No sori

• Function: Photosynthesis only

• Usually more numerous

• Often more divided/lacy

Fertile fronds:

• Have sori (spore clusters)

• May have different shape

• Sometimes more upright

• May be less divided

Recording:

• Both types present? Yes  /  No

• If yes, describe differences: _____

F. Look for Sori (Spore Clusters)

CRITICAL for fern identification!

What are sori? Clusters of sporangia (spore cases) on underside of fronds

Turn frond over and examine:

1. Presence:

• Present / Absent (frond may be sterile or immature)

2. Location on frond:

• Along midrib (center vein of pinna)

• Along margin (edge of pinna)

• Scattered across underside

• In distinct lines (parallel to veins)

• Covering entire underside

3. Sorus shape:

• Round dots (most common)

• Elongated dashes (kidney-shaped or linear)

• Continuous along edge

• J-shaped or horseshoe-shaped

4. Indusium (protective covering):

• Present - Looks like flap, umbrella, or hood over sorus

  • Shape: Circular  /  Kidney-shaped  /  Linear  /  Hood-like

• Absent - Sori exposed (naked)

5. Color (indicates maturity):

• Green (immature, not releasing spores yet)

• Yellow/tan (nearly mature)

• Brown (mature, releasing spores)

• Black (very mature or old)

• Orange/rust (some species)

Recording: Sori characteristics: _____

G. Examine Sori with Hand Lens

Look VERY closely (10× magnification):

Can you see individual sporangia?

• Yes - Look like tiny spheres or beans

• No - Too tightly clustered

Sporangium characteristics:

• Shape: Spherical  /  Bean-shaped (reniform)

• Stalk: Present  /  Absent (sessile)

• Annulus: Look for ring of thick-walled cells

  • This is the "catapult" that flings spores out!

  • Visible  /  Not visible

If sori are brown/mature:

• Gently tap frond over white paper

• Do spores fall out? Yes  /  No

• Spores look like fine dust (need microscope to see details)

Recording: Sporangium details: _____

H. Note Habitat Type

Where is fern growing?

• Terrestrial - Growing in soil on ground

• Epiphytic - Growing on tree (not parasitic! Just using for support)

• Rupestral - Growing on rock

• Aquatic - Growing in water

• Cultivated - Planted in landscape/pot

Recording: Habitat type: _____

I. Check Rhizome (If Accessible)

Rhizome = underground stem (this is where fronds emerge from)

If you can safely excavate (potted plant or with permission):

1. Carefully dig around base

2. Expose rhizome without destroying plant

3. Don't collect from wild plants! Just observe

Observations:

• Visible? Yes  /  No (some are very deep)

• Orientation: Horizontal  /  Vertical  /  Creeping

• Diameter: _____ mm

• Color: Black  /  Brown  /  Green

• Surface: Smooth  /  Covered in scales  /  Hairy

• Scale color (if present): _____

Recording: Rhizome characteristics: _____

J. Look for Fiddleheads

Fiddleheads (crosiers) = Coiled emerging fronds

When to find them:

• Spring (March-May in Arizona)

• After rain or watering

• In actively growing ferns

If you find fiddleheads:

• Present - Coiled young fronds visible

• Absent - Not growing season or mature plant

• Color: Bright green  /  Brown  /  Reddish  /  Silver (covered in scales)

• Number emerging: _____

• Degree of coiling: Tightly coiled  /  Partially unrolled  /  Nearly flat

• Photo these! - They're beautiful and diagnostic

• Don't disturb - These are future fronds

Recording: Fiddleheads: Present  /  Absent

Step 3: Search for Fern Allies (Rare!)

These are evolutionarily distinct from true ferns but also seedless vascular plants

Horsetails (Equisetum)

Characteristics:

• Jointed, hollow stems (like bamboo)

• Whorls of branches at nodes

• Silica in cell walls (feels rough/scratchy)

• Cone-like structures at tips (strobili)

In Arizona: VERY rare in wild, occasionally in cultivation

If you find horsetails:

Record:

• Species (if known): Equisetum _____

• Plant height: _____ cm

• Stem diameter: _____ mm

• Number of whorls per segment: _____

• Branch pattern: Branched  /  Unbranched

• Strobilus present? Yes  /  No

  • If yes, length: _____ mm, color: _____

• Texture: Rough (scratchy)  /  Smooth

• Habitat: _____

• Photos: Whole plant, close-up of nodes, strobilus

Club Mosses (Lycopodium, Selaginella)

Characteristics:

• Tiny leaves (microphylls) covering stems

• Look like large mosses but have vascular tissue

• Cone-like structures (strobili) at tips

• Branching pattern often Y-shaped

If you find club mosses:

Record:

• Type: Lycopodium (club moss)  /  Selaginella (spike moss)

• Growth form: Upright  /  Trailing  /  Cushion-forming

• Plant height/length: _____ cm

• Branching pattern: Y-shaped dichotomous  /  Irregular  /  Unbranched

• Leaf size: _____ mm (very small!)

• Leaf arrangement: Spiral  /  Four-ranked  /  Other

• Strobili present? Yes  /  No

  • If yes, length: _____ mm, position:  /  Terminal (at tip)  /  Lateral (side)

• Habitat: _____

Step 4: Data Table for Pteridophytes

Part 3: Adaptive Features Comparison

Goal: Test how different plant groups have evolved adaptations for terrestrial life through quantitative experiments.

Experiment A: Water Retention

Question: Which plant group loses water fastest when exposed to air?

Hypothesis: Bryophytes lose water fastest (no cuticle), ferns intermediate (thin cuticle), seed plants slowest (thick cuticle)

Step 1: Collect Fresh Samples

Collect small samples (thumbnail-sized) of:

• 2-3 different moss types

• 1 liverwort (if found)

• 1-2 fern fronds (small pieces from margin)

• Optional: 2-3 seed plant leaves for comparison (native desert plants)

All samples should be:

• Healthy and green

• Similar size (for fair comparison)

• Fresh (collected within last hour)

Step 2: Hydrate Fully

Procedure:

1. Spray all samples thoroughly with water

2. Let sit for 5 minutes to absorb fully

3. Samples should look plump, dark green, fully hydrated

4. Shake off excess surface water (gently!)

Ensures all start at same hydration level (100%)

Step 3: Weigh or Measure (Initial)

Weigh with scale

1. Weigh each sample on paper towel

2. Record weight in grams (0.01g precision if possible)

3. Label: "Sample 1 - Moss A - Wet weight: _____g"

Recording:

• Sample ID: _____

• Type: _____

• Initial weight/size: _____

• Time: _____

• Appearance: Fully hydrated  /  Plump  /  Dark green

Step 4: Dry in Sun

Setup:

1. Place samples on white paper in sunny, warm spot

2. Spread out - don't let samples touch (affects drying)

3. Full sun exposure

4. Good air circulation (near window or outdoors)

Timing:

• Check every 10 minutes for first 30 minutes

• Then every 15 minutes until dry

• Total time: 30-90 minutes (depends on sample size, sun intensity)

At each check:

• Note appearance changes

• Record time elapsed

• Take photos showing progression

Step 5: Reweigh/Measure (Final)

After drying period (when samples appear fully dry):

Criteria for "dry":

• Brittle, crispy texture

• Color pale or brown

• Shriveled appearance

• No flexibility

Measurements:

• Final weight/size: _____

• Time to dry: _____ minutes

• Final appearance: Shriveled  /  Crispy  /  Color changed

Step 6: Calculate Water Loss

If using scale:

Formulas:

• Water lost = Wet weight - Dry weight (grams)

• % Water loss = (Water lost ÷ Wet weight) × 100

Example:

• Moss wet weight: 0.50 g

• Moss dry weight: 0.05 g

• Water lost: 0.50 - 0.05 = 0.45 g

• % water loss: (0.45 ÷ 0.50) × 100 = 90%

Recording: % water loss: _____%

Step 7: Test Recovery

Can dried plants recover when rehydrated?

Procedure:

1. Spray dried samples generously with water

2. Start timer immediately

3. Observe closely

Record at intervals (2, 5, 10, 20, 30 minutes):

Time: _____ minutes Observations:

• Color returning? No change  /  Slight greening  /  Mostly green  /  Fully green

• Shape recovering? Still shriveled  /  Slightly plumping  /  Mostly plump  /  Fully plump

• Flexibility? Still brittle  /  Some flexibility  /  Flexible  /  Original flexibility

Record:

• Time to first visible recovery: _____ minutes

• Time to full recovery: _____ minutes (or "Did not recover")

• Did it fully recover? Yes  /  Partial  /  No

Expected pattern:

• Mosses: Recover quickly (5-15 minutes), fully

• Liverworts: Recover quickly (5-20 minutes), fully

• Ferns: Recover slowly (20-60 minutes), may not fully recover

• Seed plants: Usually don't recover (permanent wilting)

Bryophytes are poikilohydric (tolerate desiccation). Vascular plants are homoiohydric (die if dried out).

Experiment B: Structural Support Analysis

Question: How does vascular tissue and size relate to structural support?

Step 1: Measure Maximum Heights

For each group, find the TALLEST specimen you observed:

Record:

• Mosses: Height of tallest clump or sporophyte: _____ cm

• Liverworts: Height of tallest structure: _____ cm

• Ferns: Height of tallest frond: _____ cm

• Fern allies: Height of tallest plant: _____ cm (if found)

Compare:

• Which group achieves greatest height? _____

• What's the size difference? (fern ÷ moss height = _____ × taller)

Expected pattern: Ferns >> Mosses (often 10-100× taller!)

Step 2: Assess Rigidity

Test structural stiffness of each plant type

Procedure:

1. Hold base of specimen

2. Let plant extend horizontally (parallel to ground)

3. Observe how much it droops

4. Rate rigidity

Rigidity scale:

• 1 = Completely limp, cannot hold shape (falls straight down)

• 2 = Flexible, droops significantly (45-90° droop)

• 3 = Some rigidity, slight drooping (15-45° droop)

• 4 = Rigid, holds position well (<15° droop)

• 5 = Very rigid, like a stick (0° droop)

Test for each group:

• Moss stem: Rigidity rating: _____

• Liverwort: Rigidity rating: _____

• Fern frond (petiole): Rigidity rating: _____

• Fern ally stem: Rigidity rating: _____ (if found)

Vascular tissue (xylem) provides lignin = structural support

Step 3: Look for Vascular Tissue

Key evolutionary innovation! Xylem and phloem allow long-distance transport

For mosses/liverworts:

1. Cut or tear stem lengthwise

2. Look closely with hand lens

3. Look for any dark strands inside stem

Expected:

• Usually absent (they lack true vascular tissue!)

• May have hydroids (water-conducting cells) in some mosses—very primitive

• No internal structure visible / Faint strands visible

Recording: Vascular tissue: Absent  /  Primitive (hydroids?)

For ferns:

1. Cut frond petiole (stalk) crosswise with razor or sharp knife

2. Make cut as clean and flat as possible

3. Look at cut surface with hand lens or camera zoom (10×)

What to look for:

• Pattern of dark dots or crescents = vascular bundles

• Arranged in circle or C-shape in cross-section

• Dark tissue = xylem (water transport)

• Light tissue surrounding = phloem (sugar transport)

Record:

• Present - Clear vascular bundles visible

• Pattern: Circular dots  /  C-shaped arc  /  Other: _____

• Number of bundles: _____

• Bundle diameter: _____ mm

• Sketch what you see!

Step 4: Measure Stem/Rhizome Diameter

Thickness correlates with structural support

Measure:

• Moss: Main stem thickness: _____ mm (very thin, <1 mm usually)

• Liverwort: Thallus thickness: _____ mm (very thin)

• Fern: Rhizome diameter: _____ mm (5-30 mm typically)

  • Also measure petiole diameter: _____ mm

• Fern ally: Stem diameter: _____ mm (if found)

Pattern: Larger diameter = more support tissue = can grow taller

Experiment C: Reproductive Structure Comparison

Goal: Compare spore production strategies across plant groups

Step 1: Sketch Reproductive Structures

Create detailed scientific drawings:

For each structure, include:

• Overall shape

• Size (measure and include scale bar)

• Labels for all parts

• Notes on color, texture

• Magnification used

Draw:

1. Moss sporophyte:

• Whole structure (seta + capsule + calyptra)

• Close-up of capsule showing peristome teeth (if visible)

• Label: seta, capsule, operculum, calyptra, peristome

2. Liverwort archegoniophore (if found):

• Umbrella-like structure

• Rays and stalk

• Label: rays, stalk, base

3. Fern sorus:

• Cluster of sporangia

• Individual sporangium (if visible)

• Label: sporangium, indusium (if present), annulus
  
  
  
  

4. Fern ally strobilus (if found):

• Cone-like structure

• Label: sporophylls, axis

Step 2: Measure Size

Quantify reproductive investment:

Moss capsule:

• Length: _____ mm

• Width: _____ mm

• Total sporophyte height (seta + capsule): _____ mm

Fern sorus:

• Diameter: _____ mm

• Number of sporangia per sorus: _____ (estimate if >20)

Height of spore release above ground:

• Moss: Capsule height above substrate: _____ cm

• Fern: Frond height (sori on underside): _____ cm

Why measure height? Higher release = farther dispersal by wind

Step 3: Estimate Spore Numbers

Rough calculation of reproductive output:

For ferns:

1. Count sori on one frond: _____ sori

2. Each sorus has approximately 50-100 sporangia (use 50 for estimate)

3. Each sporangium contains approximately 64 spores (typical for ferns)

4. Estimated total spores per frond = (# sori) × 50 × 64

Example:

• 100 sori per frond

• 100 × 50 × 64 = 320,000 spores per frond!

Your calculation: _____ spores per frond

For mosses:

• Each capsule produces approximately 10,000-1,000,000 spores depending on species

• Typical estimate: 50,000 spores per capsule

Compare:

• One moss capsule: ~50,000 spores

• One fern frond: ~200,000-500,000 spores

• Ferns produce MORE spores per structure

Ferns are larger, more resources available. But mosses have many capsules per patch.

Step 4: Data Tables

Water Retention Data:

Structural Support Data:

Reproductive Structure Data:

Part 4: Microhabitat Characterization

Goal: Understand the specific environmental requirements of different plant groups.

Question: Do different plant groups occupy different microhabitats (niches)?

Step 1: Return to Collection Sites

Visit each location where you collected specimens

Bring:

• Thermometer

• pH test strips

• Measuring tape

• Notebook

• Camera

Step 2: Measure Environmental Factors

For EACH collection site, record these data:

A. Light Level

Measure light intensity:

Quantitative (light meter app):

• Light intensity: _____ lux

Expected pattern:

• Mosses: Prefer shade to deep shade

• Liverworts: Prefer deep shade

• Ferns: Partial shade to shade

• Exceptions exist!

B. Moisture Level

Use squeeze test (see Lab 7):

1. Dig down 2-3 inches near plant

2. Grab handful of substrate

3. Squeeze firmly

4. Classify:

Categories:

• Dry - Powdery, no cohesion, plants may be crispy

• Moist - Damp, forms ball, plants green

• Wet - Soggy, water visible, plants saturated

• Saturated - Standing water, constantly wet

Also note:

• Source of moisture: Rain  /  Irrigation  /  Seepage  /  Stream  /  Condensation

• Permanence: Constant  /  Seasonal  /  After rain only

C. Substrate Type

What is plant growing on/in?

Soil:

• Sand (gritty, large particles)

• Clay (sticky when wet, hard when dry)

• Loam (balanced, crumbly)

• Organic (rich, dark, peaty)

Rock:

• Sandstone (grainy, porous)

• Granite (hard, crystalline)

• Limestone (may fizz with acid—alkaline!)

• Basalt (dark, volcanic)

• Other: _____

Wood:

• Fresh (recently fallen)

• Partly rotted (somewhat soft)

• Very rotten (crumbly, soft)

D. Temperature

Measure air temperature at plant height:

Procedure:

1. Hold thermometer at level of plants (not in sun!)

2. Wait 2 minutes for accurate reading

3. Record in °C

Record:

• Air temperature: (_____ °C)

• Time of measurement: _____

E. Distance to Water Source

How far to nearest permanent water?

Measure or estimate:

• Stream, pond, spring, wetland

• Distance: _____ meters

• Use pacing, maps, or GPS

Expected pattern:

• Bryophytes: Usually <10 m from water

• Ferns: Can be >50 m if soil stays moist

• Both groups rare far from water in Arizona

F. Air Movement

Assess wind exposure:

Categories:

• Still - No breeze, sheltered

• Light - Occasional gentle breeze

• Breezy - Consistent gentle wind

• Windy - Strong, constant wind

Why it matters:

• Wind increases evaporation

• Bryophytes prefer still air (less drying)

• Sheltered microsites retain moisture

Step 3: Create Niche Profiles

For each species/type, summarize preferred conditions:

Format:

• Light:

• Moisture:

• Substrate:

• Temperature:

• Distance to water:

• Air movement:

• Conclusion:

Create profiles for each of your collections

Step 4: Data Table