BIOL 317 LECTURE NOTES – WEEK 3 SUMMARY BASAL ANGIOSPERMS, BASAL EUDICOTS, FAGALES; PLANT BREEDING SYSTEMS Dichotomous Key - a progressive series of paired alternative statements that lead to the identification of an organism. Keys don’t need to be dichotomous, but usually are - written keys start with a certain bit of information and progress towards an end; interactive computer keys (becoming more widespread) can start with any information. Usually most useful keys are artificial, in the sense that if you draw a dichotomous tree reflecting the branches in the key, the branches would not be monophyletic groups (a key that discriminates between monophyletic groups is called a synoptical key). Leads may pair “this” vs. “that”, or may pair “this” vs. “not this” - read carefully! If more than one character is described in a lead, the most important or consistent difference is usually listed first. The most “primitive” flowering plants may be either herbaceous or woody. These all have monocolpate pollen and two cotyledons. Near the base of the angiosperm tree are three groups of plants that are shrubs or herbs, including Amborella (one sp. from New Caledonia), Nymphaeales (water lilies), and a few odd genera from around the world grouped together in Austrobaileyales (the “ANITA grade”, or A-N-A grade). Also near the base is one lineage (Chloranthaceae) that is mostly herbaceous (along with the water lilies and monocots, these were sometimes called the “paleoherbs” – a polyphyletic group). Finally, there is a lineage called the Magnoliids (incl. Magnoliales and Laurales). Together with the members of the ANITA grade and the Chloranthaceae, these are often referred to as the “basal angiosperms”. The remaining species (more than 90%) of flowering plants belong to two sister clades: the monocots, and the eudicots (or tricolpates). Monocots are monophyletic and derived from dicots - some shared derived characters include: single cotyledon, scattered vascular bundles, parallel leaf venation (with exceptions in a few species). However, they do have pollen with a single aperture. Eudicots are monophyletic and include most of the species of flowering plants. Eudicots share the derived character of pollen grains with three apertures (tricolpate pollen). However, they do have two cotyledons. Within the eudicots; there are three large monophyletic groups and several small groups at the base: “Basal eudicots” refers to the paraphyletic grade of lineages near the base of the eudicot tree (incl. Ranunculales). Caryophyllids - this group is pretty well characterized by some distinctive features, including pigments known as betalains and seed nutritive tissue called perisperm. Flowers are polypetalous. Recent evidence places this group sister to the asterids, but historically the relationships between the caryophyllids and other groups have not been well understood. Rosids in the broad sense - contains most other polypetalous families. This group is difficult to characterize morphologically; defined mostly by the absence of traits found in other groups. Asterids in the broad sense - contains most of the gamopetalous families; characterized best by embryonic and chemical characters. Magnoliids and “basal eudicots” share some traits that are interpreted as “primitive” in angiosperms: gynoecium usually composed of unfused carpels (simple pistils); superior ovary; sepals and petals often not differentiated (tepals). The textbook has more information on each family; see “readings” on the class website for list of suggested reading assignments. Magnoliales - Magnoliaceae (2 gen/220 spp) – Magnolia family. (1) Woody trees or shrubs; may be evergreen or deciduous. (2) Ethereal (aromatic) oils – ‘primitive’ smell when leaves are crushed. (3) simple leaves with pinnate venation and entire margin. (4) large showy flowers, actinomorphic - always bisexual - many parts, spirally arranged; borne on elongate receptacle - sepals and petals poorly differentiated (tepals) - laminar stamens anther and filament poorly differentiated - ovary superior - fruit usually a follicle (often many aggregated together - Magnolia) or samara (Liriodendron). Laurales - Lauraceae - most well-known family of Laurales (very diverse in tropics; 50 gen/2500 spp) – Laurel family. Known for ethereal oils, includes: Laurus nobilis - bay; Cinnamomum zeylandica - cinnamon; C. camphora - camphor; Persea americana – avocado. (1) Trees or shrubs (occasionally vines); may be evergreen or deciduous. (2) Ethereal (aromatic) oils – ‘primitive’ smell when leaves are crushed. (3) Leaves simple (occasionally lobed), alternate and spiral, entire, pinnate veination. (4) Flowers bisexual or unisexual (then dioecious), actinomorphic, usually small - tepals usually 6 - stamens 3-12 (in whorls of 3) - anthers opening by 2-4 flaps (valvate anthers) - one carpel with single ovule - ovary superior - fruit a drupe, or occasionally a one-seeded berry. “Basal eudicots” have tricolpate pollen, thereby placing them firmly with the other ‘higher’ dicots we call eudicots (or tricolpates). Ranunculales - Ranunculaceae (47 gen/2000 spp) – Buttercup family. This family is difficult to characterize, because of tremendous variation, but it can be recognized by a combination of characters. (1) Usually herbs; sometimes vines or shrubs. (2) Leaves simple to deeply lobed, or compound. (3) Flowers highly variable - usually hermaphroditic (with bisexual flowers), some dioecious (with unisexual flowers) - can be radially or bilaterally symmetrical - parts spirally arranged or in whorls of 5 - petals and sepals both showy, or petals reduced/missing; petals often with nectary - ovary always superior - stamens numerous, spirally arranged - carpels usually numerous and separate, occasionally only one - fruit a follicle, achene, or berry. Ranunculales - Berberidaceae (15 gen/650 spp) – Barberry family. (1) Perennial herbs or shrubs (woody derived from herbaceous), evergreen or deciduous. (2) Leaves simple or compound (simple derived from compound). (3) Fl. parts in whorls of 3, or occasionally in 4 - sepals and petals usually 6 each and similar - stamens usually 6 (but may be 4 or many) with valvate anthers with 2 valves - single carpel; stigma often with 3 lobes (sometimes interpreted as a 3 fused carpels) - fruit usually a berry; sometimes a follicle. Rosidae sensu lato – this large group includes a great amount of variety, including two prominent families of north-temperate wind-pollinated trees belonging to the order Fagales. Wind-Pollination Syndrome: a suite of traits that wind pollinated plants often share in common. Results from convergent evolution. Flowers appear before leaves are out; flowers often in catkins (dangling inflorescence of unisexual flowers) or spikelets; plants often with separate staminate and pistillate flowers (plants monoecious or dioecious) – this permits a greater investment in male function than would be possible in hermaphroditic flowers; large number of flowers (especially males); big stamens produce lots of pollen; stigmas large and plumose or roughened (papillate) to catch pollen; ratio of pollen to ovules VERY HIGH (up to 6,000 to 1); individual flowers small and inconspicuous - without parts for attraction; flowers without scents or rewards for pollinators. Fagales - Fagaceae (9 gen/900 spp) – Oak family. (1) Trees or shrubs - mostly northern hemisphere, temperate to subtropical. (2) Leaves simple, alternate. (3) Flowers unisexual; plants monoecious - tepals usually 6; always very reduced - male flowers in catkins; 4-40 stamens per flower - female flowers solitary, or clustered in leaf axils, or at base of catkin - carpels typically 3, connate; surrounded by an involucre of many overlapping bracts; this structure is often described as a “cupule” - ovary inferior - of 3 fused carpels, each with 2 ovules; in fruit, all but one ovule aborts - fruit: nut (animal dispersed). Fagales - Betulaceae (6 gen/157 spp) – Birch family. (1) Trees or shrubs - mostly north temperate. (2) Leaves simple, alternate, usually with doubly serrate margins. (3) Flowers unisexual; plants monoecious - flowers subtended by bracts (1 main bract subtends the inflorescence with typically 2 bracteoles subtending each flower) - flowers of both sexes usually in catkins (sometimes female flowers solitary e.g., Corylus - hazel) - tepals 1-4, sometimes lacking and always very reduced - stamens 1-4 - ovary inferior; carpels 2 fused - fruit: nut (animal dispersed), samara (wind dispersed), or achene. Plant Breeding Systems Plants are incapable of reproductive “behavior” in the sense that animals behave to find and select mates. However, they have evolved a much greater array of reproductive systems because: (1) most flowering plants are bisexual (2) sexual expression can vary over time and space (3) plants rely on intermediary agents to transfer pollen (containing the sperm) (4) plants have less rigidly controlled developmental systems and can reproduce vegetatively from many parts. Asexual reproduction - reproduction of genetically identical individuals from a single parent plant. Rare in vertebrates; although it is quite common in insects (e.g., aphids), where it still involves the reproductive system (parthenogenesis). Asexual reproduction offers a competitive advantage to individuals particularly well-adapted to the local environment, because all offspring will be genetically identical to their parent. Asexual reproduction can be divided into two basic mechanisms: (1) vegetative reproduction - starting new plants from vegetative