P LANT D IVERSITY II Chapter 30

F ERTILIZATION OF S EED P LANTS V IA P OLLEN Microspore develop into pollen grains, the male gametophyte covered by sporopollenin Carried by wind or animals Pollination when pollen reaches ovule part of plant Pollen grain germinates and produces a pollen tube Two sperm released into female gametophyte Allows fertilization across long distances Water film no longer necessary Some gymnosperms retain flagellated condition of sperm, though no longer necessary

T HE S EED P LANTS A seed is an embryo and its food supply that is surrounded by a protective coat Able to survive away from parent plant Can remain dormant for different periods of time Dominant producers on land Enormous impact on human society

S EED P LANTS H AVE R EDUCED G AMETOPHYTES Develop from spores kept in sporangia of parental sporophyte Nutrients from parent Protects seed from environmental stresses

Most seedless plants are homosporous Produces 1 hermaphroditic gametophyte Seed plants are heterosporous Produce mega- and microsporangia Female and male spores Seed Plants are Heterosporous

S EED P LANTS P RODUCE O VULES Consists of the megasporangium, megaspore, and integuments Layer of sporophyte tissue to envelop and protect the megasporangium Gymnosperms with 1 integument Angiosperms with 2 integuments Female gemetophyte from megaspore produce 1+ eggs

G YMNOSPERMS Naked seed plants Ovules and seeds on develop of surfaces of leaves, usually as cones ( strobili ) Four phyla with uncertain relationships Phylum Cycadophyta Large cones and palm-like leaves Phylum Gnetophyta 3 genera: Welwitschia (largest leaves), Ephedra (ephedrine), and Gnetum (tropical plants that resemble angiosperms) Phylum Ginkophyta Ginkgo biloba only surviving species Ornamental species, but only males planted due to seed odor Phylum Coniferophyta Largest phyla commonly called conifers Most are evergreens and retain leaves year round, others are deciduous

P HYLUM C ONIFEROPHYTA L

L IFE C YCLE OF A P INE Pine tree is a sporophyte Separate types of cones for each gametophyte Pollen cones undergo meiosis to develop pollen grains Ovulate cone with many scales, each with 2 ovules Haploid cells produced become megaspores with some developing into gametophytes 3 years for cones to form mature seeds Ovulate cone separates and seeds dispersed by wind

A NGIOSPERMS Reproductive structures are flowers and fruits Seeds contained in fruits, the mature ovaries Most diverse and widespread plants All placed in phylum Anthophyta Previously divided into monocots and dicots 1 or 2 cotyledons, seed leaves, in embryo respectively Monocots form a clade, but most dicots now eudicots Rest of ‘dicots’ as basal angiosperms (oldest) and magnoliids Water lilies and kudzuu

F LOWERS Specialized structure with up to 4 circles of modified leaves Sepals at base, usually green, and enclose bud before opening Petals brightly colored and aid in attracting pollinators Stamens are sporophylls that produce microspores = pollen Filament is the stalk and anther is the terminal sac Carpals are sporophylls that produce megaspores Stigma is sticky and receives pollen Style leads to ovary at base with ovules

F RUITS Mature ovaries resulting from thicken ovary walls Triggered by hormonal changes Wall is the pericarp Forms only following pollination Can be fleshy or dry Pericarp softens as ripens or adheres to seed coat Adapted to disperse seeds Winged seed by wind Modified burrs to cling to animals Edible so animals eat, but seed passes unharmed with natural fertilizer

A NGIOSPERM L IFE C YCLE Pollen grains develop in anthers of stamens 2 haploid cells produced: 1 to sperm other to pollen tube Ovule develops into embryo sac Few cells: 1 is egg Anther releases pollen to sticky stigma on carpel Some flowers self- pollinate, but many cross-pollinate Stamens and carpels develop at different times or arrangement unlikely Pollen tube into style to penetrate ovule integument 1 sperm fertilizes egg = 2n zygote 1 sperm into other cells to form endosperm, becomes food source for embryo Embryo with basic root and cotyledons

H UMAN D EPENDENCE ON S EED P LANTS Most food from angiosperms Wheat, rice, maize, potatoes, cassava, and sweet potatoes contribute 80% of human calorie consumption Angiosperms feed livestock Other foods Coffee, tea, cocoa, and spices Sources of wood and medicines