Lecture 5: Euphyllophytes

Question 1

What are the principle characteristics of euphyllophytes?

Answer 1

• sister group of lycophytes
• roots of monopodial
• lateral roots to develop
• sporophytic leaves - euphylls with branched vein system,
• growth by means of marginal or apical meristems
• independent evolution of euphylls via planation (flattening of branches) and webbing
• stem vasculature of moniphytes often sphonostele

Question 2

describe the roots of eyphyllophytes

Answer 2

roots of monopodial

• not dichotomously branched, with exarch protoxylem (to the outside of phloem)

Question 3

Describe the leaves of ephyllophytes

Answer 3

sporophytic leave called euphylls

• with branched vein system
• mesophyll among veins
• leaf gap

Question 4

Describe the evolution of euphylls

Answer 4

via planatation (flattening of branches) and webbing (connection of branch system with mesophyllic material) of lateral branch system of ancestors

Question 5

Describe the stem vasculature of moniplophytes

Answer 5

often siphonostele (cylinder of conducting tissue surrounding a central core of pith in certain stems)

• central parenchym atous pith, xylem surrounded by phloem

Question 6

what is a pith

Answer 6

central core of unspecialized cells surrounded by conducting tissue in stems

Question 7

What branches belong to euphyllophytes?

Answer 7

• spore producting monilophytes: ferns and horsetails
• seed producting spermatophytes: seeds plants (gymnopserms and angiosperms)

Question 8

What is the difference between eurosporangium and leptosporangium

Answer 8

Eurosporangiate sporangia:

• relatively large,
• derived from several epidermal cells,
• wall of more than one cell layer;
• many spores (100s to many 1000s);
• no specialized dehiscence mechanism;
• no stalk

Leptosporangia:

• developing from a single cell,
• 1-layered sporangium wall,
• clustered into sori/ opening with annulus;
• usually just 64 spores, dehisce via an annulus, stalked

 Eurosporangium… older lineages (whisk ferns, ophioglossid ferns, marattioid ferns and horsetails

 Leptosporangium … more diverse and specious polypodiopsids

Question 9

Which one is common to phylogenetically older lineagesone is common to phylogenetically older lineages

Answer 9

eusporangium

Question 10

Briefly describe a horsetail

Answer 10

• Rhizomatous perennial herbs
• Rigid hollow stems with siliceous epidermal cells and internal canals
• Leaves microphyllous, non-photosynthetic
• Peltate sporangiophores in terminal strobili, bearing homosporous sporangia, spores green with hygroscopic elaters

Question 11

What are lignophytes?

Answer 11

polysporangiate embryophytes

Question 12

Describe characteristics of lignophytes (woody plants)

Answer 12

• monopodial growth (single stem and lateral branches)
• characterized by: secondary growth of lateral meristems (cambia)
• vascular cambia giving rise to wood (secondary xylem and phloem; building annual wood rings)
• cork cambium giving rise to cork (cork + cork cambium) = periderm)

Question 13

How did early lignophytes propogate?

Answer 13

Early existinct lignophytes üby means of spores

Question 14

How did fern like lignophytes (pteridosperms) propogate?

Answer 14

already produced seeds

Question 15

What are seeds?

Answer 15

embryo surrounded by nutritive tissue within seed coat, usually consists of precursors of mature organs

Question 16

What do seeds serve as?

Answer 16

• protection, dispersal, nutrition of gerrminating embryo, might function in dormancy mechanisms

Question 17

Describe the development of eustelic vasculature

Answer 17

Vasculature of seed plants

• single ring of discrete vascular bundles, protoxylem endarch

Question 18

Describe difference of seeds and spores

Answer 18

spores:

• meiotically originated, haploid, unicellular, mostly little nutritive reserves, weak protection, no structures for dispersal
  
  • non-vascular plants, lycophytes, ferns, progymnosperms

seeds:

• multicellular, embryo + protective tissue, food reserves, protection, dormancy, specialized structures for dispersal
  
  • seed ferns, seed plants

Question 19

Describe female gametophyte development

Answer 19

• Pollination droplet: secreted by young ovule through micropyle, pollen grains attached
• Delivery of pollen grains to the ovule (=pollination), fertilization (temporally segregated in gymnosperms)
• Meiosis of megasporocyte (spore mother cell)
• Of the 4 haploid spores, 3 abort, one gives rise to reduced female gametophyte
• Megaspore not released from sporangium but retained within megasporangium – endosporic female gametophyte expands (mitotic divisions), archegonia may differentiate (gymnosperms)
• Evolution of integument (protective tissue) and micropyle – entry site for pollen grains
• Fertilization occurs
• Zygote divides and differentiates into embryo
• Female gametophyte tissue nurtures the embryo, integument matures into seed coat

Question 20

Describe male gametophyte development

Answer 20

Endosporic, growing into exosporic pollen tube which releases motile (in some gymnosperms) or non-motile (in other gymnosperms and all angiosperms) sperm cells

Question 21

What can we say about the whole gametophyte development in seed plants

Answer 21

Whole gametophyte development in seed plants is highly reduced, endosporic, represented by pollen grains (male) or nutritive tissue nurturing the young embryo (gymnosperm)