BIOL 1030 – TOPIC 7 LECTURE NOTESTopic 7: Angiosperms, Flowers and Pollination Syndromes – Phylum Anthophyta (Chs. 30, 38)Ι. Phylum Anthophyta – flowering plants (antho – flower)A. also known as angiosperms (angeion – vessel or enclosure; sperma – seed)B. ovules enclosed within carpel (parent diploid sporophytic tissue) at pollination1. the “vessel” is the carpel, which is a modified leaf2. carpels, especially their enlarged basal portion (the ovary), usually develop into fruit, which is unique to angiospermsC. about 250,000 known living species (dominant photosynthetic organisms on land)D. predominant source of human foodE. most widespread and diverse plant phylum1. range from microscopic to plants with leaves over 6 m long2. flowers show incredible variety from species to species3. variety of lifestyles includes parasites (ex.: mistletoe, dodder, beechdrops); mycotrophs (derive nutrients from fungi; ex.: Indian Pipe, others); epiphytes (ex.: some orchids); “carnivorous” (ex. pitcher plants, sundews, Venus flytrap)F. monophyletic group with seeds, refined xylem, double fertilization, and these synapomorphic characteristics:1. seed contains endosperm2. presence of flowers (modified stems and leaves)3. true fruitsG. evolutionary history1. monophyletic group2. origin about 140 MYAH. phylogeny1. historically divided into two classes, dicots and monocots• recent genetic analysis has shown that the traditional dicots are a paraphyletic group• thus, the old classification scheme is being replaced2. no conclusive cladogram has been produced for angiosperms• studies are ongoing• most modern cladograms have Amborella and water lilies as a sister group (or groups) to the rest of the angiosperms• cladogram below from http://tolweb.org/tree?group=Angiosperms&contgroup=Spermatopsida1 of 9BIOL 1030 – TOPIC 7 LECTURE NOTES• various class-level groupings have been proposed, the overall naming and formal classification within Phylum Anthophyta is still in a state of flux• nevertheless, by far most of the living angiosperm species are found within two monophyletic groups, eudicots and monocots3. eudicots• most have embryos have two cotyledons (seed leaves)• leaves have netlike veins• flower part typically in multiples of 4 or 5• groups of vascular tissues in a ring• pollen grains mostly with 3 or more apertures• endosperm mostly used up in mature eudicot seeds• about 175,000 living species; includes nearly all flowering trees and shrubs• about a sixth are annuals (entire growth cycle in one year or less)4. monocots• embryos have one cotyledon• leaves have essentially parallel veins• flower part typically in multiples of 3• groups of vascular tissues scattered• pollen grains mostly with one aperture• endosperm typically present in mature monocot seeds• about 65,000 living species; no true wood, few annualsΙΙ. Why were (and are) angiosperms successful?A. 130 MYA two major continental masses1. Laurasia = North America, Europe, Asia2. Gondwanaland = South America, Africa, Australia, Antarctica, India, New Zealand)B. angiosperms first appeared in Gondwanaland, in what was likely a drier interior regionC. advantages of flowering plants1. transfer of pollen over great distances promotes outcrossing2. efficient seed dispersal via fruit3. endosperm gives seedlings a fast start4. leaves appropriate for fast growth in hot, dry environmentD. coevolution with insects1. dominant by ~80 MYA, second half of Cretaceous Period2. all present angiosperm families represented by that time3. many insect orders appeared or became more abundant at that timeΙΙΙ. Flowers2 of 9BIOL 1030 – TOPIC 7 LECTURE NOTESA. modified stems with modified leavesB. develop as primordium bud at end of stalk called pedicelC. pedicel widens at tip to form receptacleD. other flower parts attached to receptacle in four whorls; from outside in:1. calyx – sepals; usually green, leaf-like, and protect immature flower2. corolla – petals; usually colorful, attract pollinators; together with calyx called perianth3. androecium – stamens; male reproductive structures• filament + anther• microspores produced within anther, shed as pollen4. gynoecium – female reproductive structure• center location is most protected• formed from leaf-like structure with ovules along margin• edges fold inwards around ovules, forming carpels primitive: many separate carpels advanced: carpels fused (called pistil)• carpel/pistil segments ovary – swollen base with 1 to hundreds of ovules; develops into fruit stigma – tip; sticky and/or feathery to catch pollen style – usually present; separates stigma from ovary• nectaries may be present at base of pistil; secrete sugar, amino acids, and other compounds to attract pollinatorsE. know the structures of a flower [Figure 38.2] and their functions 3 of 9BIOL 1030 – TOPIC 7 LECTURE NOTESΙς. typical Angiosperm life cycleA. female gametophyte1. single diploid megaspore mother cell in ovule undergoes meiosis while flower develops2. of 4 haploid megaspores produced, usually 3 break down3. remaining megaspore expands and replicates and divides until there are 8 haploid nuclei in two groups of 44. one nuclei from each group migrates toward center; these are polar nuclei5. polar nuclei usually fuse to make a diploid nucleus, but may remain separate – in either case, they wind up in a single cell6. cell walls form around other nuclei, creating the 7-celled, 8-nucleate embryo sac or megagametophyte (female gametophyte)7. meanwhile, two layers (integuments) of ovule develop into seed coat with micropyle (small opening)8. in the megagametophyte, one of the cells closest to the micropyle becomes the egg; the other two there are synergids9. the three cells on the other end (the antipodals) eventually break downB. male gametophyte1. anthers with patches of tissue that become chambers lined with nutritive cells2. each patch has many diploid microspore mother cells3. microspore mother cell undergoes meiosis, making 4 haploid microspores that typically remain grouped in a tetrad4. each microspore nucleus replicates and divides once (via mitosis) without cytokinesis (meaning they remain as one cell with two nuclei, a binucleate microspore)5. usually, tetrad then breaks up6. two-layered wall develops around each binucleate microspore, now called a pollen grain• outer wall – sculptured, appearance usually species-specific,