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Home , Eudicots, Fagales

BIOL 317 LECTURE NOTES – WEEK 3 SUMMARY

BASAL ANGIOSPERMS, , ; 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 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 may be either herbaceous or woody. These all have monocolpate and two cotyledons. Near the base of the angiosperm tree are three groups of plants that are shrubs or herbs, including (one sp. from New Caledonia), (water lilies), and a few odd genera from around the world grouped together in (the “ANITA grade”, or A-N-A grade). Also near the base is one lineage () 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 (incl. and ). Together with the members of the ANITA grade and the Chloranthaceae, these are often referred to as the “”.

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 , scattered vascular bundles, parallel 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. ). Caryophyllids - this group is pretty well characterized by some distinctive features, including pigments known as betalains and seed nutritive tissue called perisperm. are polypetalous. Recent evidence places this group sister to the , but historically the relationships between the caryophyllids and other groups have not been well understood. 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; and 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 or shrubs; may be evergreen or deciduous. (2) Ethereal (aromatic) oils – ‘primitive’ smell when 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 - (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 - (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; 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 (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 - (9 gen/900 spp) – 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 - female flowers solitary, or clustered in leaf axils, or at base of - 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: (animal dispersed).

Fagales - (6 gen/157 spp) – 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 - ) - 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 parts of another plant, eg. rhizomes/stolons and layering (stems rooting at nodes), tillers (lateral shoots at base of plants that produce adventitious roots), bulblets (little bulbs from the base of big bulbs), bulbils (bulb-like propagules, can arise in leaf axils and/or replace the flowers), cuttings (severed branches can root and form new plants); (2) apomixis - normal sexual reproduction is replaced by asexual reproduction eg. agamospermy: production of seeds that are genetically identical to parent. Dandelion ( officinale) is the best known example.

Sexual reproduction - production of offspring following the fertilization of an egg by a sperm, which itself follows pollination in seed plants. Offspring will NOT be genetically identical to their parent.

Hermaphroditic and monoecious flowering plants may either: cross-pollinate and cross-fertilize (outcrossing) – prevents selfing and the expression of deleterious genes that are heterozygous in parent – reduces inbreeding depression (but allows build-up of deleterious alleles) – increases genetic exchange of material; brings favorable alleles together OR self-pollinate and self-fertilize (selfing). Self-pollination between different flowers = geitonogamy; within a flower = autogamy (flowering plants). Self- fertilization is also referred to as autogamy (all organisms). Recombination and random assortment of chromosomes still occur in meiosis, introducing variation, although genetic diversity is lost over time (inbreeding results in loss of heterozygosity).

To self-fertilize, a plant must be self-compatible (SC) – pollen from same plant can germinate, grow, and ultimately deliver sperm to egg of same plant. Selfing can insure seed set, if no neighbors or pollinators are available. Selective advantage to selfing - transmits both sets of genes to offspring; selective disadvantage to selfing - increases inbreeding depression. The advantage of selfing (2X genetic contribution to offspring) must be offset by a cost of inbreeding depression of at least 50%, in order to favor outcrossing. Cleistogamy - in a few plant species there are flowers that never open and are only capable of self-fertilization (as in some violets), because there is no mechanism for pollen to disperse. Some plants will produce both cleistogamous and chasmogamous (showy, outcrossing) flowers; offspring may come from selfing and outcrossing.

Many flowering plants are capable of self-fertilization and many are habitual selfers (~20% of angiosperms). Others (majority of flowering plants) have evolved many ways to discourage self-pollination or to prevent it entirely: – Self-incompatibility (SI) - a biochemical reaction in the stigma, style, or (rarely) ovary rejects self pollen and prevents pollen tube growth or entry into the ovule. Ancestral angiosperms were self-compatible and SI has evolved many times, but SC has evolved from SI plants many times, too. – Unisexual flowers: dioecy and monoecy prohibit or inhibit selfing, respectively. – Physical separation of stamens and stigma (herkogamy), eg. heteromorphic flowers (called distyly or tristyly), which have long filaments and short styles on some flowers and short filaments and long styles on others. Darwin studied distyly in . – Temporal separation of stamen and stigma maturation (dichogamy): protandry (anthers dehisce and release pollen before stigma is receptive), protogyny (stigma is receptive to pollen before anthers mature).

Certain traits tend to be characteristic of breeding system: Selfers: • SC • Mostly annuals • Few, inconspicuous flowers • Similar maturation of reproductive parts – Anthers near stigma – Style included • All fruits mature • Low pollen:ovule ratio

Outcrossers: • SI or SC • Mostly woody perennials • Numerous large, showy flowers • Differential maturation of reproductive parts – Anthers far from stigma – Stigma well-exserted • Only some fruits mature • High pollen:ovule ratio