Greek: angeion case; sperma seed By far the most diverse group of plants that has ever existed with more than 240,000 different species. The angiosperms

Why are there so many speciesOrigin of angiospermsTime scale Mosses Ferns Angiosperms Why are there so many species?

Gondwana Gondwanaland Angiosperms probably originated in the tropics West Gondwana, equivalent to modern South America plus Africa

1. Leaves have finely divided venation 6. Generally hermaphrodite flowers and cross pollinating (70%) 4. Ovules protected within an enclosed structure 5. Double fertilization to produce diploid zygote and triploid endosperm nucleus 2. Xylem contains vessels as well as tracheids and parenchyma 3. Phloem contains sieve elements with companion cells Principal differences between Gymnosperms and Angiosperms

Examples Grasses Triticum, wheat Zea mays corn lillies Oak trees, Quercus Coleus Lycopersicon, tomato Potato, Solanum tuberosum Monocotyledons and Dicotyledons

Typically veins are distributed such that mesophyll cells are close to is a vein. The network of veins also provides a supportive framework for the leaf. Angio-Gymno 1. Leaves have finely divided venation Coleus leaf cleared of cell contents and with xylem stained A dicotyledon

Leaf of a monocotyledon plant The major venation follows the long axis of the leaf and there are numerous joining cross veins so that, as with the dicotyledon, mesophyll cells are always close to a vein.

Diagram of a dicot leaf

Tomato leaf Upper epidermis Lower epidermis Pallisade parenchyma: chloroplasts visible around cell periphery Spongy parenchyma Longitudinal section through a vascular bundle Xylem vessel: annular thickening around cell wall Phloem Bundle Sheath

Ficus leaf Lower epidermis Pallisade parenchyma Spongy parenchyma Vascular bundle Ficus, the fig, is a xerophyte Collenchyma forming a hypodermis Collenchyma above and below the vascular bundle

Leaf cross section of Bouteloua Bulliform cells Bundle sheath cells with chloroplasts Parenchyma with chloroplasts Phloem Xylem Lower epidermis Upper epidermis Sclerified fibers Collenchyma

… C3 and C4 photosynthesis?

Leaf cross section of Zea mays ("corn"). Bulliform cells Bundle sheath cells with chloroplasts Parenchyma with chloroplasts Phloem Xylem Lower epidermis Upper epidermis

Bundle sheath cells filled with chloroplasts. CALVIN REACTION SITE Xylem Phloem Parenchyma filled with chloroplasts C4 acids synthesized in the parenchyma move to the bundle sheath Carbon skeleton compounds return to parenchyma Anatomical separation of the C4 photosynthesis component processes

Angio-Gymno 2. Xylem contains vessels as well as tracheids and parenchyma Angio-Gymno 3. Phloem contains sieve elements with companion cells Ways in which Angiosperms are different from Gymnosperms

Angiosperm xylem and phloem In Angiosperms Xylem and Phloem contain more specialized cells than in Gymnosperms as well as containing Fibers and Parenchyma. Xylem: Vessel Elements Phloem: Sieve elements, Companion cells

Vessels Elongated vessel element: This cell provides moderate support and fluid conduction. Vessel Tracheid Wide vessel element: This kind of cell is better for fluid conduction than physical support. These vessel elements have completely perforated end walls Tracheids provide better support but less slower rates of water conduction than vessels A vessel is composed of several vessel elements Tracheids lack perforation plates but their end walls contain numerous pits.

Phloem STMs and CCs develop from the same progenitor cell. STMs, are columnar cells and unite vertically to form a Sieve Tube. STMs have no nucleus at maturity and depend on CC to regulate physiological processes. Each STM has one to several CC. The Sieve Plate is analogous to a Perforation Plate in vessels. Sieve Tube Members (STM) Sieve plate Cucurbita phloem Companion Cells (CC) (cucumber)

Stems as diverse as slender vines, fat cacti, or as modified as potato tubers all have this organization, but with various zones modified. Cacti are so wide because they have an exceptionally thick cortex. Potato tubers have a gigantic pith and almost no wood. Dicotyledon stem cross section Angelica stem transverse section is typical of a dicotyledon plant without secondary thickening. Four zones: 1) epidermis 2) cortex, in many species the outermost part is a hypodermis 3) ring of vascular tissues, usually a ring of vascular bundles 4) pith. J. D. Mauseth We eat Angelica in confectionary

Transverse section of corn stem, Zea mays. There are four parts: 1) epidermis 2) cortex with or without part differentiated into a hypodermis 3) vascular bundles 4) a matrix of parenchyma called conjunctive tissue or pith This is the organization of monocot stems: numerous vascular bundles distributed throughout a tissue that may be either parenchyma or collenchyma Vascular bundles

17.10, 31.2 through 31.6 Courses that deal with this topic Sections you need to have read Botany 443 Origins of our modern floras