BIOL 317 LECTURE NOTES – WEEK 5 SUMMARY ROSIDS: MALVIDS & FABIDS Rosidae. Together with Asteridae, this clade contains most of the species of eudicots. We have already covered several families of rosids; this week we will finish our treatment of rosid families. Brassicales - Brassicaceae (419 gen/4130 spp) – Mustard family (or cabbage family). Also called “Cruciferae” - one of ten families that has two accepted names, this family gets its traditional name from the ‘cross-shaped’ petal arrangement. Brassicaceae includes many economically important plants e.g., Brassica oleracea - the following are “cultivars” arising from and maintained by artificial selection: var. capitata – cabbage; var. botritus – cauliflower; var. gemmifera - brussels sprouts; var. italica – broccoli; var. acephala – kale. (1) Herbaceous. (2) Glucosinolates – secondary compounds stored in plant vacuoles. These are released from the vacuole when damage occurs to the cell (e.g., from insects chewing on the leaf) and are altered by the enzyme myrosinase to produce compounds called isothiocyanates (“mustard oils”). Mustard oils give characteristic smell and taste. Secondary compounds in plants usually function to deter insect herbivores. (3) Flowers very uniform in floral structure - 4-parted actinomorphic calyx and corolla - stamens 6 (or many) often tetradynamous (4+2; 4 long inner and 2 short outer) in traditional Brassicaceae s.s. - carpels two, fused, ovary superior with a ‘replum’ (term for a false septum with thickened marginal rim, specific to this family), separating the two locules - ovules attached parietally to margins of replum - fruits typically a capsule called either a silicle (<2X longer than wide) or silique (>2X longer than wide). Some earlier-diverging members of the family have different types of flowers and fruits; these do not occur significantly in our area. Arabidopsis thaliana is the most widely-studied model system in plants. It is fast- growing, easily propagated and maintained in laboratory settings, and has a small genome (5 chromosomes; 135 Mb). Arabidopsis is the model for much of our knowledge of plant genetics, development, physiology, etc. Its complete genome sequence was published in 2000; the first plant genome sequenced. Malvales - Malvaceae (204 gen/2330 spp) – Mallow family. Includes cotton, okra, Hibiscus, cacao. (1) Mostly herbs in North America; also shrubs and trees. (2) Leaves simple, palmately veined, often lobed or compound. (3) Stellate or branched hairs. (4) Mucilaginous cells (e.g., makes okra ‘slimy’); mucilage probably functions to deter insect herbivores. (5) Flowers 5 parted - stamens (5-) many, often +/- fused by the filaments into one or more clusters; when connate at the filaments to form a tube around the style then called monadelphous - ovary superior - placentation axile - carpels usually 5 (sometimes 2 or many) - fruit usually a capsule. Domestic cotton - Gossypium hirsutum - is tetraploid, believed to be of hybrid origin (resulting from a hybridization between an African and a S. American species). Polyploidy is common in plants, but complicates genomic sequencing efforts; the genome of what is believed to be a wild (diploid) precursor of domestic cotton (Gossypium raimondii) was published in 2012. Malpighiales - Salicaceae s.s. (2 gen/485 spp) – Willow, poplar family. Salix – willows; Populus – poplars, cottonwoods, aspen. The abbreviation “s.s.” stands for “sensu stricto”, latin for “in the strict sense”. Salicaceae has been expanded dramatically to include most of Flacourtiaceae, a primarily tropical family with much more diverse morphology. Salicaceae as covered here is monophyletic and is nested within Flacourtiaceae (similar to the Aceraceae derived from within Sapindaceae). Like Aceraceae/Sapindaceae, we will learn the characteristics of the smaller, derived group that is significant in temperate North America. (1) Shrubs and trees; vegetative reproduction by root sprouts (e.g., aspen groves) or rooting of branches (e.g.,willows along streams) is common. The largest single living ‘organism’ is an aspen grove in Utah (Populus tremuloides), nicknamed “Pando”. (2) Leaves simple, with ‘salicoid teeth’ (vein ending at tip of tooth with a small gland). (3) Dioecious - separate male and female plants. Pando is a male grove. (4) Flowers in catkins (both male and female) - fls borne in axil of hairy bracts on catkin-like axis (not always pendent) - no perianth (a nectar gland or cup-like bract may be interpreted as calyx) - ovary superior, with 2-4 fused carpels with many ovules (different from oaks and birches, which are inferior and with 1-few ovules) - fruit a capsule. (4) Seeds hairy - hence “cottonwood”. Not related to cotton! Black cottonwood (Populus trichocarpa) is an important timber species, native to the PNW, and the foremost model system for studying woody plants. Its genome sequence was published in 2006; the first tree genome. Malpighiales - Violaceae (22 gen/950 spp) – violet family. (1) Herbs in temperate parts of the world, but most of the species of Violaceae are tropical trees. (2) Leaves simple (often cordate at base). (3) Flowers zygomorphic (bilaterally symmetric) - petals 5, the lower one forming a ‘spur’ - stamens five, the lower two forming a nectary (held within the petal spur) - ovary superior - placentation parietal - 3 fused carpels - fruit a capsule. Violets often have two different kinds of flowers on the same plant: Chasmogamous - large showy flowers that typically are cross-pollinated. Cleistogamous - small inconspicuous flowers that don’t open and are self- pollinated in the bud. Both of these represent sexual reproduction, but one typically outcrosses and the other typically self-fertilizes. This way, violets can benefit from the advantages of both (reproductive assurance from selfing; genetic diversity from outcrossing). Last two families are pretty closely related, even though they may seem rather different. They form an interesting contrast. In one, Rosaceae, the flowers are all pretty much alike, but fruit types differ greatly and form the basis of subfamilial divisions, whereas in the other, Fabaceae, fruit types are all similar - the legume - but flowers differ greatly and form the basis of subfamilies. Fabales - Fabaceae (642 gen/18,000 spp) – pea or legume family. Also called “Leguminosae”, from the distinctive fruit which is characteristic of all its members. The third-largest family of plants; very economically important, contains many food species (pulses), as well as forage species, timber species, medicinal plants, gums, and dyes (eg. indigo). (1) Mostly woody tropical trees, but in temperate zone mostly herbs. (2) Commonly associated with N-fixing bacteria as symbionts in root nodules. This increases access to important nitrogenous nutrients, making legumes good colonizers of nutrient poor environments, and good cover crops or rotation crops. (3) Leaves usually compound - margins entire - stipules often present. (4) Flowers fall into three basic floral types - zygomorphic (subfams. Caesalpinioideae and Faboideae) or actinomorphic (Mimosoideae) - sepals and petals in 5s - stamens: 10 unfused (subfam. Caesalpinoideae), 10 partly fused, 9 fused and 1 free (diadelphous) (subfam. Faboideae), or many unfused (subfam. Mimosoideae) - ovary superior - fruit a legume (specific type of follicle: dry, dehiscent fruit derived from a single carpel, opening along two lines of dehiscence). The zygomorphic floral type is called a “flag” flower; it is most characteristic of Faboideae, in which the two lower petals are fused to form a “keel”. Caesalpinoid flowers sometimes have a “flag” form, but the lower petals are NOT fused and the stamens are NOT fused. Mimosoid flowers (actinomorphic) are called “brush” flowers, because they have many stamens that are exerted on long filaments and form a brush that covers visiting insects or birds with pollen. Banner 1 free stamen Flag Flower wing wing 9 fused stamens keel Subfamily Caesalpinoideae is ancestral (paraphyletic) within the Fabaceae, and subfamilies Mimosoideae and Papilionoideae are monophyletic (derived from Caesalpinoid ancestors). Rosales - Rosaceae (95 gen/2825 spp) – Rose family. (1) Plants woody or herbaceous. (2) Leaves simple or compound (palmate or more commonly pinnate) - stipules usually present - leaves/leaflets often with serrate margins - alternate arrangement. (3) Flowers actinomorphic - sepals and petals in 5s - stamens many - hypanthium usually present - ovary superior, inferior, or half inferior. Most striking variation in reproductive morphology is in fruit type. Traditional view of subfamilies is based on fruit type. Spiraeoideae: usually 5 free carpels (5 simple pistils) -> follicle Rosoideae: many free carpels (many simple pistils) -> aggregate fruits (unusual, accessory fruits in the case of strawberry and rose; achenes embedded in fleshy parts derived from swollen receptacle or hypanthium) Amygdaloideae: 1 carpel (1 simple pistil) -> drupe Maloideae: 2-5 fused carpels (1 compound pistil) -> pome (fleshy part derived from swollen hypanthium) Traditional subfamilies Amygdaloideae and Pomoideae (Maloideae) are monophyletic; most of the species of Rosoideae form a monophyletic clade also. However, Spiraeoideae is paraphyletic, with Amygdaloideae and Maloideae derived within it. For more practice with the concepts involved in phylogeny-based classification, try the supplementary exercises on Fabaceae and Rosaceae phylogeny and classification. Pollination biology – Sexual Encounters of the Floral