BIOL 317: Plant Identification and Classification Summer 2016 - Notes Week 7 – Tuesday Plant Speciation (cont.) • Reproductive isolation • Allopatry § genetic differences accumulated while populations are in allopatry may result in genetic barriers to gene flow without mating barriers, i.e. individuals from different populations can still mate but the result of mating does not promote the merging of the populations’ gene pools • inviable offspring - hybrid offspring do not develop properly • sterile offspring - hybrid offspring do not make gametes • less fit offspring - hybrid offspring have a combination of traits from parents that make them less adapted to their environment § if populations later meet, they may: • hybridize - genetic differences do not affect the ability of populations to successfully mate, and the populations merge and remain a single species • have mating barriers - genetic differences result in morphological and ecological differences that prevent individuals from different populations from mating • have genetic barriers - genetic differences cause hybrid offspring to be inviable, sterile, or less fit o In this case, mating barriers become adaptive and may be selected for (reinforcement), so individuals do not waste resources on mating events that produce unfit offspring • Other modes of speciation (especially common in plants) § Polyploidization - increase in the number of sets of chromosomes, e.g. from diploid (2 sets) to tetraploid (4 sets) • may result in instantaneous speciation since individuals of different ploidy levels usually cannot successfully interbreed § Hybridization - hybrid offspring may persist but be unable to mate with either parent species, thus forming a new species • hybrid offspring are often sterile due to chromosomal incompatibilities between parental genomes, but hybrid plants may persist by asexual reproduction • polyploidization in hybrids often results in regained fertility, so hybrids may reproduce sexually Core Asterids • comprises two large clades, the lamiids and the campanulids • commonly shared traits: • 5-merous flower • gamopetalous corolla • epipetalous stamens • single whorl of stamens, so number of stamens is equal to or less than number of petals/corolla lobes • 2 fused carpels • Lamiids • Solanales • another important family is Convolvulaceae (morning-glory) • Solanaceae (nightshade/tomato family) • 102 genera, 2460 spp. • distributed widely, but especially diverse in New World tropics • herbaceous or woody (shrubs) • leaves – simple, but can be deeply divided; alternate • alkaloids – used for herbivore defense, but also co-opted by humans for medicinal, narcotic, and culinary uses (e.g. atropine, nicotine, capsaicin) • flowers • usually actinomorphic • sepals 5, fused • petals 5, fused § often highly fused, with little or no free lobes § often plicate - crease lines where petals were folded when in bud • stamens 5, epipetalous • pistil compound (2 carpels); ovary superior § stigma often capitate • fruit: berry or capsule • genus Solanum • ~1400 spp. • corolla often rotate (disk- or wheel-shaped) • anthers connivent (held close together to form tube around pistil) • anthers with poricidal dehiscence • includes PNW wildflower (Nicotiana attenuata - coyote tobacco), weeds (Solanum dulcamara - bittersweet nightshade, Solanum nigra - black nightshade, etc.), food crops (Solanum tuberosum - potato, Solanum lycopersicum - tomato, Solanum melongena - eggplant, Capsicum annuum - chili and bell peppers, Physalis philadelphica - tomatillo, etc.), drug crops (Nicotiana tabacum - tobacco, Atropa belladonna - belladonna [source of atropine], etc.), and ornamentals (Solanum crispum - Chilean potato vine, Petunia spp., Nicotiana spp. - flowering tobacco, Brugmansia spp. - angel’s trumpet, etc.) • Boraginales • the relationship of this group with others in the lamiids is still uncertain • Boraginaceae (forget-me-not/borage family) • 148 genera, 2755 spp. • distributed worldwide • herbaceous [usual habit in temperate zone] or woody (shrubs or trees, common in tropics) • leaves – simple, but can be deeply divided; alternate • hispid hairs – stiff hairs with calcified or silicified walls make plants rough to the touch • inflorescence - scorpioid cyme, one-sided and coiled when flowers are in bud • flowers • actinomorphic • sepals 5 • petals 5, fused • stamens 5, epipetalous • pistil compound (2 carpels); ovary superior • subfamily Boraginoideae • corolla often with corona - raised ring on corolla, often of different color • stamens included (does not extend beyond corolla) • 2 ovules/carpel; ovules deeply divided, forming 4-lobed ovary • fruit: schizocarp, forming 4 nutlets • subfamily Hydrophylloideae • corolla without corona • stamens exserted (extend beyond corolla) • many ovules/carpel; ovary unlobed • fruit: capsule • Older classifications separated this group into several families, including Boraginaceae sensu stricto and Hydrophyllaceae, but both were found to be non- monophyletic as traditionally circumscribed. In order to make monophyletic families, Boraginaceae was expanded to include other closely related groups, including Hydrophyllaceae. • includes PNW wildflowers (Myosotis spp. - forget-me-not, Mertensia spp. - bluebells, Amsinckia spp. - fiddleneck, Hackelia spp. - stickseed, Hydrophyllum spp. - waterleaf, Phacelia spp., etc.), herbs (Borago officinalis - borage, Symphytum officinale - comfrey, etc.) and ornamentals (Pulmonaria spp. - lungwort, Cynoglossum spp. - hound’s- tongue, etc.) • Gentianales • other important families include Rubiaceae (coffee) and Gentianaceae (gentian) • Apocynaceae (dogbane family) • 415 genera, 4555 spp. • distributed widely, but especially diverse in tropics and subtropics • herbaceous or woody (shrubs or trees) • leaves – simple, opposite • milky latex • flowers • actinomorphic • sepals 5, fused • petals 5, fused § often with contorted lobes • stamens 5, epipetalous § anthers often connivent • pistils simple, 2; ovary superior § fused above ovary - at style or stigma § stylar head - pistil apex expanded • often modified for specialized pollination - anthers deposit pollen on top, stigmatic surface is on underside of head • fruit: aggregate (pair) of follicles, berries, or drupes • subfamily Asclepiadoideae • corona - 5th whorl of floral structures develop from part of stamens § in genus Asclepias, forms whorl of hoods (cup-like structures holding nectar) and horns (horn-like structures growing out of hoods) • gynostegium - fusion of stamens and stylar head • pollinia - pollen produced in coherent masses that are transferred as an unit • Older classifications separated this group into two families, Apocynaceae sensu stricto and Asclepiadaceae, but Apocynaceae s.s. was found to be paraphyletic with respect to Asclepiadaceae. In order to make monophyletic families, Apocynaceae was expanded to include both families. • includes PNW wildflowers (Apocynum spp. - dogbane, Asclepias spp. - milkweed, etc.) and ornamentals (Vinca minor - periwinkle, Catharanthus roseus - Madagascar periwinkle, Plumeria rubra - frangipani, Asclepias spp., etc.) Plant reproduction and breeding systems • Differences between plant and animal lifestyle and development Plants Animals sessile - must rely on intermediary for usually mobile transfer of male gametes body plan modular body plan fixed sexual expression can be dynamic over sexual expression fixed space and time usually bisexual usually unisexual • Asexual reproduction - produces genetically identical offspring (clones) • Vegetative reproduction - does not involve typically sexual organs (flower, fruit) • specialized structures: § rhizome - underground horizontally growing stem § stolon - aboveground horizontally growing stem § stems rooting/cuttings - detached stems can grow adventitious roots § layering - long, drooping branches can grow adventitious roots where they contact the ground § bulblets - daughter bulbs grows off of and detach from mother bulb § bulbils - daughter plantlets grow off of mother plant; can develop on leaves, in place of flowers, etc. • especially common in Salicaceae, Crassulaceae, among other groups • Agamospermy/apomixis • production of embryo in seed via mitosis of diploid cell in parent • common in Taraxacum officinale - dandelion Week 7 – Thursday Plant reproduction and breeding systems (cont.) • Sexual reproduction - offspring is result of combination of genes from maternal and paternal parents • pollination (transfer of pollen grain from anther to stigma) precedes fertilization (fusion of sperm and egg) • Selfing/autogamy - pollination and fertilization by gametes from same individual • cleistogamy - adaptation to promote selfing within individual flowers § non-showy, closed flowers • Outcrossing - pollination and fertilization by gametes from different individuals - Adaptations to promote outcrossing: • self-incompatibility § biochemical reaction prevents pollen grain from germinating and growing on stigma of same individual (and other individuals with same alleles as pollen grain at S-locus) • dichogamy - temporal separation of sexes § protandry - anthers mature before stigma is receptive § protogyny - stigma is receptive before anthers mature • herkogamy - spatial separation of sexes § heterostyly - different individuals of same species have flowers of different morphs: stigma above anthers, or anthers above stigma § unisexual flowers • plants can be monoecious or dioecious • Advantages of different breeding systems • asexual reproduction and selfing § reproductive