Learning Objectives Of over 400 families of angiosperms, some 80 of them fall into a single clade, called monocots because their seeds have only a single cotyledon. The remainder have seeds that produce two cotyledons (Figure ). This group includes some early diverging…
Seeds represent one of the most important innovations in plant evolution: a protected, nutrient-supplied embryo with the ability to await appropriate conditions for germination. Seeds and pollen allowed plants to limit their reliance on water for completion of their life…
Learning Objectives Angiosperms have a complex life cycle. The gametophytes have been further reduced: antheridia were lost in the gymnosperms and archegonia were lost in the angiosperms. Both gametophytes are now housed within the flower, a structure composed of highly…
Learning Objectives Flowers are sets of highly modified leaves that function to attract a pollinator or, if no animal pollinator is used, to optimize spore dispersal in some way. Over the course of evolutionary history and coevolution, this has lead…
Learning Objectives At the end of the Permian period, there was the largest mass extinction this planet has ever experienced. It is estimated that 96% of species that lived at that time went extinct. This event signaled the downturn for…
Learning Objectives Though the gnetophytes have been difficult to place, phylogenetically, recent genetic studies place them as sister to the Pinaceae (pine family, emerging from within the conifers. See this open-access paper for recent genetic work on the evolutionary relationships between gymnosperms.…
Learning Objectives Ginkgophyta As of 2019, the most recent genetic studies have placed ginkgos as the oldest of the extant gymnosperms. This does not mean that it was the first gymnosperm. From the fossil record, it seems that most early…
Learning Objectives Toward the end of the Carboniferous period, major changes in the climate occurred. The current day European and North American continents slammed together, forming the Appalachian mountains (which were taller, at that time, than the present-day Himalayas). Fossil…
Learning Objectives Fossil from the Devonian period reveal fernlike plants that were heterosporous; that is, produced two kinds of spores: microspores and megaspores. The megaspores were not released from the parent sporophyte. Fertilization took place within the tissue of the parent sporophyte thus freed…
The characteristics of early plants can be interpreted best as evolutionary adaptations to life outside of water (a waxy cuticle, stomata, decay- and desiccation-resistant sporopollenin) and a new harsh landscape (multicellular gametangia, matrotrophy, mutualistic symbioses with bacteria and fungi). As…