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Published byMarianna Allison Modified over 5 years ago
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Characteristics of the two groups of non-seed (seedless) vascular plants
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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
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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
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Lycophyta- Lycopodium
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Lycopodium spp
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Lycophyta: Lycopodium strobilus-homosporous
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Lycophyta: Selaginella
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Lycophyta: Selaginella strobilus-heterosporous
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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
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Horse tails: Equisetum sp
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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
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Whisk fern- Psilotum sp
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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)
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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
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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
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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
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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.
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Life cycles Generalized cycle of homosporous non-seed vascular plants
(See pg 622, LIFE) Generalized cycle of heterosporous non-seed vascular plants
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