Lycophyta, Psilotophyta Lab 10 Lycophyta, Psilotophyta

Vascular plants General features of the land plants Common name: Vascular plants Synonyms: Tracheophyta Growth habit: Multicellular: stems, leaves, and roots; thalloid gametophytes Undulipodia (“flagella”): Whiplash (2 to 1000+) Conductive cells: Sieve cells, forming phloem (food), and tracheids, forming xylem (water)

Vascular plants Clonal reproduction: Vegetative, various multicellular propagules Sexual reproduction: Homosporous or heterosporous Included Phyla: Lycophyta, Psilotophyta, Sphenophyta, Pterophyta, Cycadophyta, Ginkgophyta, Coniferophyta, Gnetophyta, Anthophyta Recognized by: Free-living, branched Sporophytes; xylem

Tetrads This slide refers to the ping-pong ball models.

Lycophyta General features of the vascular plants Common name: Club mosses (applies also to the Class Lycopodiopsida) Synonyms: None Sporophyte growth habit: Stems, leaves, roots Gametophyte growth habit: Photosynthetic or parasitic thalli

Lycophyta Stele: Protostele Undulipodia (“flagella”): Two or more whiplash Sexual reproduction: Homosporous or heterosporous Representative genera: Isoetes, Lycopodium, Selaginella Recognized by: Meiosporangia on upper surfaces of sporophylls

P Lycopodium Lycophyta: Lycopodiopsida This photo shows strobili and a vegetative stem. Other species don’t have organized strobili; instead, any leaf can be a sporophyll. Lycophyta: Lycopodiopsida

A Lycopodium stem Lycophyta: Lycopodiopsida The ring of large, thick-walled cells is part of the cortex. The vascular bundle is inside that—the xylem cells are darker and more distinct than the phloem cells. Lycophyta: Lycopodiopsida

A Lycopodium strobilus Lower left: Preserved strobili. Top: Stereoscope view of an entire sectioned strobilus. Lower right: Close-up of sporophylls and meiosporangia. Lycophyta: Lycopodiopsida

P Selaginella Lycophyta: Selaginellopsida The bluish cast on the leaves is the result of a light interference phenomenon in the cuticle that seems to enhance light capture in dim environments. Some Selaginella species from the tropics appear more blue than green. Lycophyta: Selaginellopsida

D Selaginella “resurrection plant” This species is found in the Chihuahuan Desert of northern México and western Texas. In the native habitat, the plants have an extensive root system, which is removed in the lab examples. Lycophyta: Selaginellopsida

A Selaginella “sporeling” This is called a “sporeling” by a poor analogy with a seedling, but it is actually an embryonic sporophyte emerging from a female gametophyte, still inside its megaspore cell wall. Tiny male gametophytes still cling to it. In nature, the male gametophytes need not be this close, but these slides were made from plants grown in cultivation. Lycophyta: Selaginellopsida

D Selaginella strobilus If you look closely at a dark sporangium, you can see the four megaspores. The lighter sporangia contain the microspores. Lycophyta: Selaginellopsida

A Selaginella strobilus Upper left: Stereoscope view, showing entire strobilus. Right: low magnification, showing megasporangia and microsporangia. Lower left: Close-up of megasporangium, showing two of the four spores, with their trilete marks sectioned. Lycophyta: Selaginellopsida

D Isoetes Lycophyta: Isoetopsida Since there isn’t a good specimen of Isoetes, students are not responsible for it—it is there just so they can see more or less what the plant looks like. Lycophyta: Isoetopsida

D Isoetes megaspores and microspores The large white spore with the trilete mark is a megaspore. The small tan grains clinging to it (by electrostatic attraction—this wouldn’t normally occur in nature), and to the piece of sporophyll on the right, are microspores. They look like grains of sand, but they are actually much smaller. Lycophyta: Isoetopsida

Psilotophyta General features of the vascular plants Common name: Whisk ferns Synonyms: Psilophyta Sporophyte growth habit: Stems Gametophyte growth habit: parasitic branching thalli

Psilotophyta Stele: Protostele Undulipodia (“flagella”): Two or more whiplash Sexual reproduction: Homosporous Representative genera: Psilotum, Tmesipteris Recognized by: No leaves or roots; dichotomous branching; synangia

P Psilotum Psilotophyta Left: Top portion of a Psilotum plant, showing the synangia. Right: Close-up of the synangia, each one in the axil of a prophyll, which is probably a modified leaf. Note the dichotomous branching. Psilotophyta

D Psilotum rhizomes Psilotophyta Note the dichotomous branching and apical meristems of this rhizome. The hairs are rhizoids. Psilotophyta

A Psilotum rhizome Psilotophyta The red blotches surrounding the stele are the Casparian strip, which marks the endodermis. Note that there is more phloem than xylem in this underground, food-storing rhizome. Psilotophyta

A Psilotum meiosporangium On the left is the aerial stem and on the right is a synangium which is attached to it below the plane of this section. Note the meiospores in each chamber of the synangium. Psilotophyta

Appearances can be deceiving Contrast the trilete mark of the spore on the left with the three dividing walls of the sporangium, top right. Although they look similar, they are different structures. On the lower right is an intact synangium, showing that the dividing walls are internal structures.