Characteristics of the two groups of non-seed (seedless) vascular plants

1) Lycophyta Commonly known as club mosses Sporophyta dominant Leaves small arranged spirally, with vascular tissue called microphylls 2 types of stele present: Protostele (haplostele in Selaginella; actinostele & plectostele in Lycopodium) Amphiphloic siphonostele (solenostele) in Selaginella

Lycophyta… Spores produced in kidney-shaped sporangia in the axils of microphylls or in structures called strobili (strobilus) Plants may be homosporous (Lycopodium) or heterosporous (Selaginella) Gametophytes: Spores germinate to produce gametophytes containing chloroplasts Gametophytes considered autotrophic

Lycophyta- Lycopodium

Lycopodium spp

Lycophyta: Lycopodium strobilus-homosporous

Lycophyta: Selaginella

Lycophyta: Selaginella strobilus-heterosporous

2) Pteridophyta- Fern Allies Fern Allies--Whisk ferns and horse tails 1) Horse tails Sporophyte consist of stem with small, wedge-shaped leaves & arranged in whorls (groups) the stele is a eustele spores are borne in sporangia in sporangiophores arranged in terminal cones plants are homosporous, but spores develop into small female & male gametophytes represented by one living genus, Equisetum

Horse tails: Equisetum sp

2) Fern Allies-Whisk ferns Most members are extinct (known from fossils only) only two genera still living, Psilotum & Tmesipteris Sporophyte consists of dichotomous branches with small leaf-like appendages appendages are not supplied with vascular tissues Rhizomes (subterranean stems) present Stele a protostele (actinostele) vascular tissue found in the stem only

Whisk fern- Psilotum sp

Fern Allies- Whisk ferns Fertile aerial shoots bear tri-lobed structures called synangia Synangia develop on enlarged apices of short lateral branches results from fusion of 3 sporangia Members are homosporous Spores germinate to give achlorophyllous gametophytes considered to be nutritionally saprophytic Both archegonia & antheridia develop on the same gametophyte (monoecious)

Homospory vs heterospory Plants which bear one type of spores are called homosporous plants Usually produce a single type of gametophyte With male and female reproductive organs (antheridia and archegonia) Homospory only limited to early primitive plants Heterospory: Plants with two distinct types of spores are called heterosporous

Heterospory… Sporophyte of heterosporous plants produce small spores (microspores) and large spores (megaspores) A large number of microspores are produced in microsporangia protected by microsporophylls Small microspores develop into male gametophytes or microgametophytes

Heterospory… Sporophyte produces megaspores in megasporangia protected by megasporophylls Megaspores develop into female gametophytes or megagametophytes Only few, (4) megaspores are produced in a megasporangium

Heterospory Gametophytes develop inside the spore walls; gametophytes reduced & well protected Heterospory evolved in many plant groups Heterospory appeared to give selective advantage to the plants Considered to set a stage towards the evolution of the seed.

Life cycles Generalized cycle of homosporous non-seed vascular plants (See pg 622, LIFE) Generalized cycle of heterosporous non-seed vascular plants