EKU General Botany Lab

Vascular Cryptogams

(Nonseed Vascular Plants)

The plant groups for today's lab sometimes are called vascular cryptogams. Cryptogams means having hidden gametes - no seeds, flowers or fruits.

In nonseed vascular plants, the sporophyte (diploid) phase of the life cycle is always dominant. The gametophyte is nonvascular, and may be either photosynthetic or dependent on fungi. Many of these plant groups are ancient--the earliest vascular plant fossils are more than 420 million years old. Vascular plants have several significant adaptations that helped them succeed on land more successfully than plants that do not have vascular tissue. (What are those special terrestrial adaptations?) Before you begin the lab study of vascular plants, it will help if you review the concepts of microphylls, megaphylls, sporophylls, homospory and heterospory, on pp. 373-376 in your textbook.

PSILOPHYTES - a phylum or not? -- the jury is still out.
This group of cryptogams formerly was thought to be a remnant of the ancestors of the first land plants, classified in the Phylum Psilophyta. However, recent data indicate that even though they are structurally very simple, they could be an offshoot from primitive ancestral ferns (Phylum Pterophyta ).

Psilotum (pronounced with a silent p -- its common name is whisk fern) is the structurally simplest vascular plant on Earth. Except for its three-parted, sporangium on a short stalk, it is very similar to fossils of the earliest land plants. Psilotum sporophytes are dichotomously branched with tiny microphylls. It has rhizomes with rhizoids, but no roots. Its gametophytes are completely dependent on fungi for nutrition. Refer to the life cycle on pp. 400-401 in the textbook.

Note the living Psilotum sporophyte. It is very easy to grow. Also note the cross section of the Psilotum sporangium under the microscope next to the sporophyte.

PHYLUM LYCOPHYTA (the Lycopods)

We will examine two members of this group. All Lycophyta have microphylls.

Lycopodium (life cycle on pp. 382-383; pictures, p. 384) is homosporous. The lycopodiums also are known as club mosses.

Selaginella (life cycle on pp. 386-387; pictures, p. 385) is heterosporous. The selaginellas also are known as spike mosses.

LYCOPHYTA SPOROPHYTES

Note the Lycopodium and Selaginella sporophytes on display on the side counter. Some of them are living and some are dried or preserved specimens. Note that the sporophytes have true roots. Lycopodium sporophytes are heavily mycorrhizal.

LYCOPHYTA FOSSILS

Note the fossils on display. Structures that may be included are stems, microphylls, roots, and strobili. These fossils came from coal deposits in Kentucky.

PERMANENT SLIDES

Compare carefully the longitudinal sections of Lycopodium strobili and Selaginella strobili (slides 12 and 13, slide box C). Be sure you can identify sporangium (of Lycopodium), microsporangium and megasporangium (of Selaginella), megaspores, microspores. What is a strobilus? What is the name of the smaller structures that make up a strobilus?

PHYLUM SPHENOPHYTA (horsetails and scouring rushes)

This is a very ancient group. Equisetum is its only surviving genus. The life history diagram is on pp. 404-405 in the textbook and pictures are on pp. 402-403. Equisetum sporophytes have underground rhizomes with roots, whorled nonphotosynthetic microphylls, silicon-impregnated cell walls, and complex, compound sporangia. The gametophytes are photosynthetic and bisexual.

Note the sporophytes of Equisetum hyemale (scouring rush) growing in the pot, and the plastomounted Equisetum arvense (horsetail) specimens. Both of these species grow wild in Kentucky.

PHYLUM PTEROPHYTA (ferns)

Ferns are the most diverse group of vascular cryptogams. Ferns have megaphylls, and may be either homosporous or heterosporous. The only ferns well study today are homosporous. The life cycle diagram is on pp. 396-397 in your textbook. Sporophyte pictures are on p. 402. Pictures of indusia [what are they?] are on p. 390. Some heterosporous ferns are pictured on p. 398.

LIVING GAMETOPHYTES

[Note: a fern gametophyte is sometimes called a prothallus or prothallium .]

Young gametophytes

If these gametophytes are the correct age, you should be able to find old spore walls, rhizoids, and antheridia .

Mature gametophytes

If these gametophytes are the correct age, you should be able to find antheridia, archegonia (neck, venter and egg), rhizoids , and possibly some swimming sperm. In older gametophytes, you might see some young sporophytes. You might even witness fertilization!

LIVING SPOROPHYTES

Examine the sporophytes on display. Note: rhizomes, megaphylls, sporophylls, sori [singular = sorus], sporangia, the presence or absence of indusia.