BOT 360F - Families of Vascular Plants

Comparison of Gymnosperms and Angiosperms

Phylogenetic relationships within and between Gymnosperms and Angiosperms have been the subject of intensive research over the past few years; some of these results are summarized HERE. In examining these trees, note where the results depict relationships between the flowering plants and the different gymnosperm groups.


 
Gymnosperms (Pinophyta) Angiosperms (Magnoliophyta)
Wood Pinus wood transverse section
Vessels absent.
Quercus wood transverse section
Vessels present.
  see also this page re the structure of wood                
Phloem Phloem mother cells develop into sieve-cells only. Phloem mother cells develop into sieve-cells and companion-cells.
Microsporangia Arranged in unisexual strobili. Arranged in bisexual (sometimes unisexual) strobili (flowers).
Megasporangia In unenclosed ovules, on megasporophylls, on compressed short shoot-bract complexes, or borne terminally on leafy shoots. In ovules enclosed by tissue of the parent sporophyte (ovary) at the apex of bisexual (sometimes unisexual) strobili (flowers).
Pollination By wind, directly to micropyle of ovule. By wind, water, and especially by animal vectors; intercepted by stigma where pollen germination occurs. Compatible pollen tubes grow through sporophytic tissue to micropyle of ovule to deliver sperm nuclei to megagametophyte.
Gametophytes Megagametophyte massive, provides nourishment for embryo (pre-fertilization provisioning); microgametophyte three to tens of cells. Megagametophyte highly reduced, 4- to 16-nucleate, derived from one, two, or four megaspores; microgametophyte of three cells.
Fertilization Double fertilization absent (except in Ephedra, Gnetum). Double fertilization present (leading to formation of endosperm plus the embryo that it nourishes); provisioning of the embryo thus takes place post-fertilization.
Angiosperm Life Cycle animation (courtesy Heather Kroening & Bio-DiTRL)
Seeds Typically unenclosed, in simple or compound cones; predominantly wind-dispersed, some animal dispersal (e.g. Taxus) . Enclosed in fruit at least until mature; dispersed via water, wind, and animals (externally, internally).
Species ca. 600. > 200,000.
Distribution, ecology Predominantly temperate zone trees, shrubs (only Cycadales exclusively tropical or subtropical). Present in virtually all biomes, and representing virtually all life forms. Size 2 x 10-3 (Lemna) to 102 m (Eucalyptus), duration 10-1 to 103 y. Photosynthetic efficiency, especially under conditions of high temperatures and limited water availability, enhanced by variants (C4, CAM) of the C3 carbon fixation pathway.
Angiosperm Phylogeny Website link

Compare the ovules of Ginkgo (at right; scale in cm), as seen in the Gymnosperm lab with those of Lilium (below, in longitudinal section; scale as indicated). The Ginkgo ovules contain a massive megagametophyte that is approximately 1 cm in diameter, and in which we were able to observe archegonia with egg cells about 0.5 mm in diameter.

In the Lilium ovules, the megaspore (left, below) develops into a few-celled megagametophyte (center, below) in which three nuclei adjacent the micropyle are analogous to an archegonium (one of them functions as an egg nucleus).

Ginkgo ovules

Lilium ovule with megaspore

The progressive reduction of the gametophyte that is seen in the seed plants is an example of neoteny or, more generally, of heterochrony. In this case (neoteny), reproductive maturity is achieved earlier and earlier in development. Compared to the perennial, woody habit, the herbaceous annual habit of many angiosperms can also be seen as an example of neoteny.

Lilium ovule with megagametophyte

Lilium philadelphicum L.

For more info on reproduction in flowering plants, including links to still more sites, click HERE.

 

Ginkgo ovules - photo: E. Harris. Lilium philadelphicum - photo: M. Ferguson. Both © 1999, 2000 Royal Ontario Museum.


Sporne (1975)

[back to top]

ditrl

| What are plant families? | How do we distinguish them? | How and why do we study them? | Selected vascular plant families of Ontario | Reading List | Course outline |

|EEB337H1 Home Page | What's New | U of T Ecology & Evolutionary Biology | University of Toronto |

© 2008 Department of Ecology & Evolutionary Biology and 2000-2006 Botany Department, University of Toronto.

Please send your comments to tim.dickinson@utoronto.ca; last updated 14-Sep-2008