BIOL 317 LECTURE NOTES – WEEK 6 SUMMARY

ASTERIDS: CORNALES, ERICALES, CAMPANULIDS

Asteridae. Together with Rosidae, this clade contains most of the species of eudicots.

Synapomorphies of Asteridae sensu lato: (1) iridoid compounds – secondary chemical compounds thought to be plant defenses; (2) unitegmic ovules – ovules covered by a single integument (integument is the outer covering of the ovule, becomes seed coat) – result of either loss or fusion of the two integuments found in all other angiosperms; (3) tenuinucellate ovules – thin nucellus in ovule (nucellus is the tissue beneath the integument that surrounds the female gametophyte).

Cornales - Cornaceae (13 gen/130 spp) – Dogwood family. Cornus is the most important genus. (1) Woody trees or shrubs (with one notable local exception, C. unalaschkensis). (2) Lvs. opposite, simple; lacking stipules; secondary veins arching from lf. base to apex, elastic with spiral thickenings; malpighiaceous hairs (2-forked). (3) Inflorescence sometimes flower-like, with enlarged, showy bracts. (4) Flowers actinomorphic - 4-parted - 2-3 fused carpels - ovary inferior - fruit a drupe.

Ericales - Ericaceae (124 gen/4100 spp) – Heather family. Very abundant in PNW. (1) Mostly trees and shrubs, some herbs. (2) Lvs simple, usually alt., often thick and leathery. (3) Plants often mycorhizal/mycotrophic (mutualistic root associations with fungi) or myco-heterotrophic (parasitic on fungi, which, in turn are dependent on other green plants); some are totally without the ability to photosynthesize (holoparasites = obligate parasites). (4) Flowers actinomorphic (sometimes zygomorphic as in Rhododendron), usually urn-shaped - 5-parted perianth, usually connate - 10 stamens (sometimes 5 in Rhododendron); sometimes epipetalous; anthers poricidal with terminal pores; often with ‘horned’ appendages - 3-5 fused carpels; nectary disk around base of ovary - fruit a berry or capsule.

Parasitic reduction syndrome (holoparasites): This combination of traits is repeated in many different groups of parasitic plants. The dramatic difference relative to other related plants that are not photosynthetic often results in segregating them into distinct families (eg, Orobanchaceae from Scrophulariaceae; Monotropaceae from Ericaceae; Lennoaceae from Boraginaceae; Cuscutaceae from Convolvulaceae; Rafflesiaceae from Euphorbiaceae). (1) Loss of leaves - leaves reduced to scales. (2) Reduced overall size of plant - no need for large plants to hold leaves. (3) Loss of roots - reduced to short, stumpy projections with haustoria. (4) Loss of chlorophyll. (5) Loss of genes needed for photosynthesis. (6) Higher substitution rate (more rapid DNA divergence) in genes that are not lost.

Ericales - Polemoniaceae (16 gen/320 spp) – Phlox family. Most diverse in western US. (1) Herbaceous, sometimes slightly woody at base (as in some species of Phlox). 2) Lvs. variable, but usually simple, alternate; sometimes opposite and sometimes divided or pinnately compound (as in Polemonium). (3) Flower morphology seems typical of traditional “core” Asteridae - 1 whorl of stamens alternate with corolla lobes and adnate to corolla - 3 fused carpels; note 3-forked style; this is very unusual in core Asteridae, but this character is fairly common in families in this part of Asteridae s.l. - fruit a capsule.

“Core asterids” generally share the following traits: (1) gamopetalous corollas – petals connate, forming a corolla tube; (2) 5 epipetalous stamens, alternate with petals – a single whorl of stamens, adnate to the corolla tube, attached in between the corolla lobes; (3) 2 fused carpels.

Campanulids. Many members of this clade have inferior ovaries, including the four campanulid families that we will learn. Small flowers arranged in conspicuous inflorescences are also common amongst campanulids, with several examples of showy, flower-like inflorescences (pseudanthium - many small flowers together making up a structure that functions as one flower).

Dipsacales - Adoxaceae (4 gen/150 spp) – Moschatel (or elderberry) family. (1) Woody or herbaceous, mainly woody in PNW. (2) Lvs. opposite; simple or compound, entire or toothed, stipules present or absent. Flowers actinomorphic, occasionally with outer flowers sterile, showy, and zygomorphic - flowers 5- parted, sepals often reduced - 3-5 fused carpels, style short, stigma capitate (not divided) - ovary inferior - fruit a drupe. Includes Sambucus and Viburnum, two genera traditionally placed in Caprifoliaceae.

Dipsacales - Caprifoliaceae (36 gen/810 spp) – Honeysuckle family. Older classification schemes (such as used in Hitchcock & Cronquist) exclude herbaceous members of this family, treating them separately as Valerianaceae and Dipsacaceae, and include two important, woody genera belonging to Adoxaceae, with radially-symmetric flowers (Sambucus and Viburnum). (1) Mostly woody, some herbaceous. (2) Lvs. opposite; usually simple, with no stipules. (3) Flowers zygomorphic (sometimes weakly so), typically 2 upper and 3 lower lobes, but sometimes with 4 upper lobes/1 lower lobe (especially in Lonicera, the honeysuckles) - 2-5 fused carpels - ovary inferior - fruit a berry, capsule, drupe, or achene.

A MAD Cap Horse: a commonly-used mnemonic to help remember the North American families of woody plants with opposite leaves. Adoxaceae, Maple (Aceraceae, now Sapindaceae), Ash (Oleaceae, not covered in this class), Dogwood (Cornaceae), Caprifoliaceae, Horse chestnut (Hippocastanaceae, now Sapindaceae, not covered in this class).

Apiales - Apiaceae (434 gen/3780 spp) – Carrot (or parsley) family. Also called Umbelliferae, “the umbels”. (1) Herbs, including many herbs/spices (dill, caraway, coriander, cumin, fennel, anise), and edible plants (carrot, celery, parsnip, parsley). (2) Often aromatic with a variety of non-iridoid secondary compounds (ethereal oils, triterpenoids, sesquiterpene lactones, etc.) (3) Lvs. alternate, simple, or (more commonly) compound; with sheathing leaf bases. (4) Typical inflorescence: umbel – many flowers with pedicels emerging from one point, subtended by bracts; or compound umbel (an umbel of umbels). (5) Flowers usually actinomorphic, sometimes the outer flowers in an inflorescence zygomorphic, acting as rays - 5-parted - polypetalous - 2 fused carpels, each with one ovule - ovary inferior - fruit a schizocarp.

These plants fit well into the Asteridae, except for the free petals; they were classified in the Rosidae in Cronquist and other systems. However, developmental studies show that the small flowers result from the cessation of development at a stage at which point the lobes of the corolla have developed, but the tube has not.

Asterales - Asteraceae (1535 gen/23,000 spp) – Sunflower family. Also called Compositae, for the “composite” flowers (heads of many small flowers aggregated into a flower-like inflorescence). The largest family of dicots. (1) All life forms, but mostly herbaceous; like Apiaceae, lacking iridoids. Many with milky sap (eg. Lactuca, lettuce, from the latin for milk). (2) Lvs. usually simple, without stipules; alt. or opp. (3) Inflorescence (pseudanthium) a capitulum or “head”, surrounded by an involucre consisting of involucral bracts (also called phyllaries). (4) Flowers borne on a flat to conical receptacle; this often with scales or chaff between the flowers. (5) Flowers - two kinds: ray florets - often female or sterile, zygomorphic, with large, 5-toothed, strap-like corolla (ligule); disk florets - usually hermaphrodite, actinomorphic, with inconspicuous corolla - calyx reduced to bristles or scales, called pappus; sometimes absent - anthers fused at margins (synantherous androecium) - ovary inferior, composed of 2 fused carpels each with one ovule, one ovule aborts, leaving a single-seeded achene (‘cypsela’ - special word for fruit of Asteraceae).

Heads with both disk florets and an outer series of ray florets are called radiate heads; most species of Asteraceae have this type of inflorescence. Some members, however, have heads with no rays, these are called discoid heads. Inflorescences composed of all ligulate florets (= rays, but hermaphrodite and fertile) are called ligulate heads.

Special pollen presentation mechanism – “pollen pump”: the style typically is 2- branched at the tip, and the stigmatic surface is along the inner wall of the split portion. When the flower matures the style forks are held together as the style emerges through the tube formed by the fused anthers, pushing the pollen before it. This exposes the pollen to pollinators BEFORE the style splits open exposing the stigmatic surface. The anthers release pollen before the stigma is receptive (protandry).

Biogeography The study of patterns of geographic variation in nature, and the processes that give rise to these patterns. Before 1750, 1% of currently described spp. were known, and the Earth was thought to be immutable (unchanging). The “age of exploration” resulted in great increase in what European scientists knew about the world; patterns in distribution of species became apparent, and the ideas of evolution and a dynamic Earth began to become prevalent.

Some important patterns in the geographic distribution of plants: (1) climate is the most important determinant of plant assemblages; (2) environmentally similar regions that are isolated from one another have distinct assemblages of plants (Buffon’s Law); (3) there is a latitudinal gradient in diversity, with species richness increasing with decreasing latitude (the tropics are more species-rich than temperate regions, such as WA).

Ecological biogeography: deals with short timescales, functional groups (communities), environmental constraints (niches). How does the environment influence plant assemblages? Because geology and landforms largely determine local climate, they are among the most important elements in determining the vegetation of a region.

Some characteristic plant communities of WA: alpine tundra - low vegetation; short, cool growing season. Subalpine - mixed forest and open meadows; short growing season, but not as short or cool as tundra. Montane forest - continuous tree canopy; species composition varies with environmental conditions (precip, temp, etc.). Temperate rainforest – forest with sufficient rainfall to sustain a heavy epiphytic plant community (eg, Pacific coast side of Olympic Peninsula and places on west slope of Cascades. Needs at least 2 meters of rainfall per year. Lowland forest - long growing season; lots of precip (30”-100”+ per year). Shrub-steppe - sagebrush and bunch grasses; low precipitation (5-20” per year).

Ecological factors contributing to the distribution of plant communities in WA: Climatic factors: The interaction of rainfall, temperature, and mountains is what controls most of our vegetation patterns in Washington. • Prevailing westerly winds bring cool moist air from over the Pacific on land in Washington. • As this cool air comes over land, it is forced to rise, first to cross the Olympic mountains and then to cross the Cascades. • Air pressure decreases as it rises, and thus cools (this is called adiabatic cooling); cool air can hold less moisture than warm air, so moisture condenses and falls as rain on the west sides of our mountains. • As the air passes the mountain crest, it drops and warms (adiabatic warming); this air now has less moisture than it did at the same elevation on the west side, and is warmer, so it can hold more moisture and has a low relative humidity. • The air moving east across eastern Washington stays at about the same elevation, so the dry air does not release much moisture as rain. However, it does pick up moisture along the way from bodies of water, the soil, and plants, so by the time it reaches the eastern edge of the state (e.g., Spokane) it has more moisture and the precipitation begins to increase again. Edaphic factors: soil type and composition; availability of soil nutrients. Biotic factors: (1) symbioses - relationships with animal pollinators/dispersers - relationships with plant/microbial associates (e.g., rhizobia; mycorrhizae; mycotrophism; host-parasite relationships). (2) Competition - stable, non- stressful environments typically have fewer species, because the evolution of strong competitors keeps others out - heterogenous (spatially and temporally) stressful environments (e.g., dry) typically have more species. (3) Succession - serial colonization by different species assemblages following disturbance, resulting in an eventual climax community. (4) Human impacts - deforestation, particularly clear-cutting, but also tree removal for development - wetland filling, especially in the Puget Sound - urbanization, ca. 70% of lowland Puget Sound forest lost in past 30 years - agriculture, mostly eastern Washington, where only very small remnants of native grassland remain - introduction of non-native species of plants and animals - climate change, decreased summer water availability and other impacts.

Historical biogeography: deals with long timescales, taxonomic groups (clades), biogeographic/earth history events. What were the processes that gave rise to present-day patterns in plant distributions? Phylogeny is an integral part of investigating historical biogeography; phylogeography is the study of relationships between organisms, and where they are found.

Historical factors contributing to the distribution of plant communities in WA: Physical factors: (1) volcanism and mountain building - plate tectonics (subduction of oceanic plate beneath continental plate) built the Cascades, and the chain of volcanoes from CA to Alaska (incl. Mt. Rainier and Mt. St. Helens). Very extensive lava flows ~20 million years ago built the Columbia plateau. (2) Glaciation - continental glaciers carved Puget Sound and deposited the hills in Seattle; as recently as 15,000 years ago, the location of Seattle was under an ice sheet thousands of feet thick. The lowland forests of Puget Sound are therefore relatively young, and probably not in equilibrium (climax community not yet reached). Extensive flooding and erosion from glacial activity carved the channels and other landscape features of the Columbia basin in WA. Biotic factors: (1) migration - dispersal ability restricts many plants that might be able to live here, enables others to arrive. (2) Evolution - divergence and diversification of new species, usually in geographic isolation; extinction of populations and species. Evolution and migration over geologic timescales are why two species in the PNW and the Amazonian rainforest might be related, and why the vegetation of the PNW is different to other parts of the world which share a similar climate.

Dispersal vs. Vicariance. Alternative hypotheses in historical biogeography to explain how species arrived at their present-day distributions. Populations of organisms may become separated via migration to new areas, and then speciate, resulting in sister species occupying different geographic ranges via dispersal. Alternatively, populations occupying a more or less continuous geographic range may become separated via the appearance of a barrier between them, and then speciate, resulting in sister species occupying different geographic ranges via vicariance. Phylogeography can be used to test these hypotheses, since a different phylogenetic tree topology may be predicted in each case.