Plant Taxonomy Introduced Species The flora of almost

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Plant Taxonomy

Plant Taxonomy

Introduced Species The flora of almost every region now contains alien or introduced plants

Introduced Species The flora of almost every region now contains alien or introduced plants - it is important to recognize them for four reasons 1. if their origin remains undiscovered, they will lead to false results in floristic studies 2. if their presence is undetected they will be mis-identified and can lead to wrongly documented experimental and observational results 3. introduced species may hybridize with native species and can create successful new species - cordgrass in England 4. introduced species can have serious (though not always harmful) ecological consequences in either natural or cultivated vegetation

Japanese Maple and Norway Maple

Japanese Maple and Norway Maple

More on Introduced Species • The British Isles have about 2500 native species; over

More on Introduced Species • The British Isles have about 2500 native species; over 5000 introduced species have been recorded • Introduced species may be casual - must be maintained or they will die out • Introduced species may become naturalized - able to maintain themselves on their own after introduction • British Isles have about 800 naturalized aliens

Japanese Cedar in Kew Garden, London, England

Japanese Cedar in Kew Garden, London, England

Even More on Introduced Species • New Zealand is home to 2065 native plant

Even More on Introduced Species • New Zealand is home to 2065 native plant species • 24, 774 non-native introduced plant species have been identified growing in New Zealand • About 2200 non-natives are naturalized and can grow on their own • The remaining 22, 000+ non-natives cannot exist outside human cultivation

Gorse (Ulex europaeus) in New Zealand

Gorse (Ulex europaeus) in New Zealand

Plant Breeding Systems • The breeding system of a plant may be defined broadly

Plant Breeding Systems • The breeding system of a plant may be defined broadly as the mode, pattern and extent to which it interbreeds with other plants of the same or of different taxa • Inbreeders are plants which predominantly or wholly produce seed from self-fertilization • Outbreeders are plants which produce seed from cross-fertilization • In nature every situation from one extreme to the other exists

Hog peanut – Amphicarpaea bracteata

Hog peanut – Amphicarpaea bracteata

Plant Breeding Systems Breeding system is taxonomically important for three reasons: 1. the extent

Plant Breeding Systems Breeding system is taxonomically important for three reasons: 1. the extent of interbreeding largely defines the pattern of variation and hence the delimitation of taxa 2. a knowledge of the breeding system frequently helps to understand taxonomic complexity, although often it does not solve problems associated with it 3. a study of the breeding system is often vital in unraveling evolutionary pathways

Plant Breeding Systems The extent to which breeding system determines variation patterns is a

Plant Breeding Systems The extent to which breeding system determines variation patterns is a point of argument at two separate levels - first (within species) the proportion of inbreeding/outbreeding within any given species is traditionally considered to determine variation within and between populations • In outbreeding species each population is variable, but similar to nearby populations, due to gene exchange between populations • Inbreeding species tend to exist as relatively uniform populations which however often differ considerably from one to another because of limited gene exchange

Ideal vs. Hybridizing Species • An ideal species is a taxonomically distinct species -

Ideal vs. Hybridizing Species • An ideal species is a taxonomically distinct species - it poses no problems and always is recognizable as a distinct entity - it does not merge with other species • This is true of many species of peas and parsleys • Species which pose taxonomic problems either hybridize with other taxa so that genetic limits are wider than morphological limits in the species • Or they have breeding barriers between members of what appears to be a morphologically recognizable taxon - these are called semi-cryptic species

Astragalus canadensis – milkvetch Fabaceae

Astragalus canadensis – milkvetch Fabaceae

Conium maculatum - poison hemlock - Apiaceae

Conium maculatum - poison hemlock - Apiaceae

Plant Hybridization • British flora probably contains 780 interspecific hybrids among vascular flora of

Plant Hybridization • British flora probably contains 780 interspecific hybrids among vascular flora of 2500 species – about 31% of all native British species • Because 2500 is 1% of world's total flora of 250, 000 flowering plants; it is possible that 78, 000 species of interspecific hybrids exist in the world or 31% of all flowering plants may be the result of interspecific hybrids

Orchidaceae – Cymbidium astronaut

Orchidaceae – Cymbidium astronaut

Consequences of Hybridization • The existence of hybrids between two species can cause practical

Consequences of Hybridization • The existence of hybrids between two species can cause practical taxonomic problems because such plants are not readily identifiable with either species - they may either have intermediate characteristics or some characteristics typical of one parent and other characteristics typical of the other parent

Quercus rubra – red oak- Fagaceae

Quercus rubra – red oak- Fagaceae

Quercus shumardii – Shumard’s oak - Fagaceae

Quercus shumardii – Shumard’s oak - Fagaceae

Hybrid oak leaves – red oak crossed with Shumard’s oak (probably)

Hybrid oak leaves – red oak crossed with Shumard’s oak (probably)

Comparison of Oak Leaves Red Oak Hybrid – Red x Shumard

Comparison of Oak Leaves Red Oak Hybrid – Red x Shumard

Hybrid pines – A. Coulter Pine, C. Jeffry Pine, B. hybrid of Coulter and

Hybrid pines – A. Coulter Pine, C. Jeffry Pine, B. hybrid of Coulter and Jeffrey

Betula occidentalis - Water birch Betulaceae

Betula occidentalis - Water birch Betulaceae

Ulmus americana - American Elm Ulmaceae

Ulmus americana - American Elm Ulmaceae

Crataegus douglasii – black hawthorn - Rosaceae

Crataegus douglasii – black hawthorn - Rosaceae

Hybrid Swarms • Fertile hybrids can lead to hybrid swarms - where by backcrossing

Hybrid Swarms • Fertile hybrids can lead to hybrid swarms - where by backcrossing with the parents and hybrid interbreeding, the parental species become connected phenetically with every possible intermediate type, so that the species can grade imperceptibly into each other • The existence of hybrid swarms indicates that there is a spectrum of ecological niches available to satisfy the requirements of a wide range of hybrid offspring or it may indicate that the hybrids do not differ in an ecologically significant trait

White Oak – Quercus alba

White Oak – Quercus alba

Oak hybrid swarm • ‘Any man who claims he can reliably identify oaks in

Oak hybrid swarm • ‘Any man who claims he can reliably identify oaks in southern Wisconsin is either a liar or a fool. ’ - John Curtis Author of the Flora of Wisconsin

Stabilization of a hybrid - Senecio cambrensis – groundsel – Asteraceae S. vulgaris

Stabilization of a hybrid - Senecio cambrensis – groundsel – Asteraceae S. vulgaris

Polyploidy

Polyploidy

Spartina alterniflora marsh – North Carolina - Poaceae

Spartina alterniflora marsh – North Carolina - Poaceae

Spartina alterniflora – Poaceae

Spartina alterniflora – Poaceae

Spartina maritima – Poaceae

Spartina maritima – Poaceae

Spartina x townsendii - Poaceae

Spartina x townsendii - Poaceae

Spartina anglica – Poaceae

Spartina anglica – Poaceae

Spartina anglica – invasive in New Zealand - Poaceae

Spartina anglica – invasive in New Zealand - Poaceae

Semi-cryptic Species • The other major taxonomic problem comes from semi-cryptic species - so-called

Semi-cryptic Species • The other major taxonomic problem comes from semi-cryptic species - so-called because their differences are marked in anatomical, chemical, cytological or (frequently) genetic characters rather than morphological characters - often they are long established species which simply do not differ greatly in gross morphology • Because of their semi-cryptic nature, there is often considerable taxonomic argument about the correct taxonomic status of these plants - should they be considered species or subspecies or something else

Eleocharis – spike rush – Cyperaceae Pollen incompatibility

Eleocharis – spike rush – Cyperaceae Pollen incompatibility

Senecio vulgaris – groundsel – Asteraceae self-pollinator

Senecio vulgaris – groundsel – Asteraceae self-pollinator

Taraxacum officinale – dandelion – Asteraceae - apomixis

Taraxacum officinale – dandelion – Asteraceae - apomixis

Apomixis is reproduction without sexual fertilization. It can happen via: • Producing seeds by

Apomixis is reproduction without sexual fertilization. It can happen via: • Producing seeds by non-sexual means (usually forming embryos directly without pollen) • Vegetative growth – plant spreads clonally

Plant Classification

Plant Classification

Process of Classification has two desirable goals: 1. The arrangement of groups into a

Process of Classification has two desirable goals: 1. The arrangement of groups into a pattern that accurately reflects their evolutionary relationships 2. The placement of groups into a reference system so their major features are easily and efficiently described and identified (information storage and retrieval)

Identification and Classification • Plant identification usually requires the use of only a few

Identification and Classification • Plant identification usually requires the use of only a few of a plant's more obvious morphological characteristics, and only one or two characteristics are usually considered at any one time as the plant is worked through the key • In plant classification (developing a logical system of organizing plants), it is necessary to consider and to evaluate all pertinent information more or less simultaneously

Conservative Characters • Flowers provide the bulk of the taxonomic information in classifying flowering

Conservative Characters • Flowers provide the bulk of the taxonomic information in classifying flowering plants this is because they tend to be conservative characters - characters which tend to remain relatively unchanged over a long period of evolutionary development and hence vary little between closely related taxa

Conservative Characters • Conservative characters are most useful in delimiting the higher taxa -

Conservative Characters • Conservative characters are most useful in delimiting the higher taxa - genera and above - in developing higher taxa, the emphasis is usually on recognition of similarity between members of the taxon • At lower levels of classification (species and below) the emphasis is more often on distinction between taxa than on clustering taxa - thus at lower levels, non-conservative characters - those which show greatest diversification, are most valuable

Flower Structure for Brassicaceae Conservative for Stamen number

Flower Structure for Brassicaceae Conservative for Stamen number

Flower Structure in Rosaceae Non-conservative for stamen number

Flower Structure in Rosaceae Non-conservative for stamen number

Good vs. Bad Characters • Taxonomists sometimes refer to characters as being "good characters"

Good vs. Bad Characters • Taxonomists sometimes refer to characters as being "good characters" or "bad characters" - these are relative terms • In general a good character is one which is constant in a taxa and allows positive identification of a taxa - good characters are therefore usually conservative • A bad character is one that is highly variable and does not allow positive identification

Flower Structure in Liliacea (left) and Iridiaceae (right) Ovary

Flower Structure in Liliacea (left) and Iridiaceae (right) Ovary

Traditional Classification • Most traditional classification systems derived from Linneaus and depend not on

Traditional Classification • Most traditional classification systems derived from Linneaus and depend not on evolutionary relationships, but rather on similarity in form or organization – taxonomic groups are based on organisms having a particular “grade” • For example the grass family Poaceae is made up of a grade of organisms having jointed stems, leaves with sheathing bases, and greatly reduced flower parts

Poaceae

Poaceae

Plant Relationships

Plant Relationships

Downy Hawthorn – Crataegus mollis

Downy Hawthorn – Crataegus mollis

White Hawthorn – Crataegus monogyna – flowers, and fruits of 4 species of Hawthorn

White Hawthorn – Crataegus monogyna – flowers, and fruits of 4 species of Hawthorn