Botany Notes: Introduction, Lecture notes for Botany and Agronomy
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Introduction to

Botany

Alexey Shipunov

February 8, 2018

Shipunov, Alexey. Introduction to Botany. Lecture notes. February 8, 2018 version. 181 pp. URL: http://ashipunov.info/shipunov/school/biol_154/

Title page: Plantago major image drawn by Alexey Shipunov.

This book was prepared at Minot State University (North Dakota, USA) with the help of students in Biology 154 and Biology 310 classes.

This book is dedicated to the public domain

Contents

Foreword 6

Glossary 7

1 Introduction to the Introduction 19 1.1 Plants, Botany, and Kingdoms . . . . . . . . . . . . . . . . . . . . . . . 19

1.1.1 Taxonomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 1.2 Styles of Life and Basic Chemistry . . . . . . . . . . . . . . . . . . . . 25

2 Photosynthesis 28 2.1 Discovery of Photosynthesis . . . . . . . . . . . . . . . . . . . . . . . . 28 2.2 Light Stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 2.3 Enzymatic Stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 2.4 C4 Pathway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 2.5 True respiration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

3 Symbiogenesis and the Plant Cell 40 3.1 Introduction to Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 3.2 Mitochondria and Chloroplasts . . . . . . . . . . . . . . . . . . . . . . 42 3.3 Cell wall, Vacuoles, and Plasmodesmata . . . . . . . . . . . . . . . . . 45 3.4 Other Parts of the Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

3.4.1 Protein Synthesis: from the Nucleus to the Ribosomes . . . . . 47 3.4.2 Other Vesicles . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 3.4.3 Cellular Skeleton . . . . . . . . . . . . . . . . . . . . . . . . . . 49

4 Multicellularity, the Cell Cycle and the Life Cycle 50 4.1 Mitosis and the Cell Cycle . . . . . . . . . . . . . . . . . . . . . . . . . 50 4.2 Syngamy and Meiosis . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

4.2.1 Sexual Process and the Syngamy . . . . . . . . . . . . . . . . . 52 4.2.2 Meiosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

3

4.3 Life cycle of the Unicellular Eukaryote . . . . . . . . . . . . . . . . . . 56 4.4 Life cycle of the Multicellular Eukaryote . . . . . . . . . . . . . . . . . 57

4.4.1 General Life Cycle . . . . . . . . . . . . . . . . . . . . . . . . . 57 4.4.2 Sporic, Zygotic and Gametic Life Cycles . . . . . . . . . . . . . 60 4.4.3 Evolution of Life Cycles . . . . . . . . . . . . . . . . . . . . . . 61 4.4.4 Life Cycle of Vegetabilia . . . . . . . . . . . . . . . . . . . . . . 63

5 Tissues and Organs; or how the Plant is built 65 5.1 Tissues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

5.1.1 Epidermis and Parenchyma . . . . . . . . . . . . . . . . . . . . 65 5.1.2 Supportive Tissues: Building Skyscrapers . . . . . . . . . . . . 66 5.1.3 Meristems: the Construction Sites . . . . . . . . . . . . . . . . 70 5.1.4 Vascular Tissues . . . . . . . . . . . . . . . . . . . . . . . . . . 70 5.1.5 Periderm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 5.1.6 Absorption Tissues . . . . . . . . . . . . . . . . . . . . . . . . . 74 5.1.7 Other Tissues . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

5.2 Organs and Organ Systems . . . . . . . . . . . . . . . . . . . . . . . . 74 5.3 The Leaf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

5.3.1 Morphology of the Leaf . . . . . . . . . . . . . . . . . . . . . . 78 5.3.2 Anatomy of the Leaf . . . . . . . . . . . . . . . . . . . . . . . . 86 5.3.3 Ecological Forms of Plants . . . . . . . . . . . . . . . . . . . . 88

5.4 The Stem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 5.4.1 Morphology of the Stem . . . . . . . . . . . . . . . . . . . . . . 89 5.4.2 Anatomy of the Primary Stem . . . . . . . . . . . . . . . . . . . 91

5.5 The Root . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 5.5.1 Morphology of the Root . . . . . . . . . . . . . . . . . . . . . . 93 5.5.2 Anatomy of the Root . . . . . . . . . . . . . . . . . . . . . . . . 96 5.5.3 Water and Sugar Transportation in Plants . . . . . . . . . . . . 97

6 Growing Diversity of Plants 101 6.1 Bryophyta: the mosses . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 6.2 Pteridophyta: the ferns . . . . . . . . . . . . . . . . . . . . . . . . . . 107

6.2.1 Diversity of pteridophytes . . . . . . . . . . . . . . . . . . . . . 107 6.2.2 Heterospory: Next step on land . . . . . . . . . . . . . . . . . . 110

7 The Origin of Trees and Seeds 115 7.1 Secondary Stem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 7.2 Branching Shoot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 7.3 Modified Shoot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 7.4 Life Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

7.4.1 Dynamic Approach . . . . . . . . . . . . . . . . . . . . . . . . . 124 7.4.2 Raunkiaer’s Approach . . . . . . . . . . . . . . . . . . . . . . . 125

4

7.4.3 Architectural Models Approach . . . . . . . . . . . . . . . . . . 126 7.5 Origin of the Seed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

7.5.1 Seed Structure and Germination . . . . . . . . . . . . . . . . . 135 7.6 Spermatophyta: seed plants . . . . . . . . . . . . . . . . . . . . . . . . 136

8 The Origin of Flowering 142 8.1 Spermatophyta 2.0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 8.2 The Flower and the Fruit . . . . . . . . . . . . . . . . . . . . . . . . . . 147

8.2.1 The Flower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 8.2.2 The Inflorescence . . . . . . . . . . . . . . . . . . . . . . . . . 155 8.2.3 Pollination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 8.2.4 The Fruit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159

8.3 Three plant families you wanted to know but were too afraid to ask . . 161 8.3.1 Leguminosae, or Fabaceae—legume family . . . . . . . . . . . 163 8.3.2 Compositae, or Asteraceae—aster family . . . . . . . . . . . . . 164 8.3.3 Gramineae, or Poaceae—grass family . . . . . . . . . . . . . . . 166

9 Plants and Earth 168 9.1 Geography of Vegetation . . . . . . . . . . . . . . . . . . . . . . . . . . 168 9.2 Geography of Vegetabilia . . . . . . . . . . . . . . . . . . . . . . . . . 169

A Methods of Taxonomy and Diagnostics 172 A.1 Cladistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 A.2 Phenetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 A.3 Dichotomous keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180

5

Foreword

While teaching botany for about twenty years, I came to the idea of re-structuring the “classical” course into a more logical sequence of themes which you will find in this textbook.

There were two main ideas that I attempted to embed here: one was to put as much plant-related information as possible into an evolutionary context, and the other was to explain complicated problems with simple words and metaphors. There are very few botany books which are trying to do the same. Among them, I would highly recommend Manetas, Ya. (2012) “Alice in the Land of Plants. Biology of Plants and their importance to Planet Earth”.

One extremely important concept to understand: plants are not animals! Obvi- ously, this phrase has many important meanings. First of all, since we humans are animals, it ismuch easier for us to understand animal life than plant life. Many terms that are associated with animal life (like “stomach” or “blood pressure”) are gener- ally well known, even intuitively. Learning botany as a beginner requires to speak about plants, and to speak, you have to learn botanical language. This is why you need to know a vast amount of terms, so be prepared to work hard.

This textbook started from students’ lecture notes but now it contains much more information. All figures are either original or modified from those sources where a license allows it (e.g., Wikimedia).

6

Glossary

K-strategy population growth when there is small number of offspring with high probability to survive

r-strategy population growth when there is huge number of offspring with low probability to survive

absorption zone root: zone of root hairs

achene one-seeded indehiscent dry fruit of Compositae, cypsella

adventitious roots originate from stem

anatomy invisible, internal structure which needs tools like a scalpel and/or mi- croscope to study

anomalous secondary growth when there aremultiple, short lived layers of cam- bium

apical meristems RAM (see) and SAM (see)

apogamy apomixis (see) when an embryo develops from unfertilized gamete, parthenogenesis

apomixis making seeds without fertilization

apospory apomixis (see) when an embryo develops from thematernal diploid tis- sue

ataktostele vascular bundles dispersed

7

bipolar plant body both root and shoot systems present

botany the scientific study of plants and plant-like organisms

brachyblasts shortened shoots of pines, larches and some other Pinaceae conifers

bract scales sterile bracts under seed scales in conifers

buds embryonic shoots

bulb short, thick underground storage shoot with prevalence of leaf tissues

calciphytes plants adapted to over-presence of CaCO3

Casparian strips part of endodermis cell walls which prevents apoplastic trans- port

central cell biggest cell of embryo sac,with two (or sometimes one) haploid nuclei

cladophylls leaf-like, flattened shoots

cleistogamous self-pollinated flowers which do not open

collenchyma living supportive tissue

companion cells nucleate “helpers” to anucleate sieve tube cells

complex tissues tissues with more than one type of cells

compound fruit fruit originated from the whole inflorescence: infrutescence

compound leaves leaves with two or more level of hierarchy

contractile roots roots which pull plant deeper in substrate

corm short, thick underground storage shoot with prevalence of stem tissues

cortex external layer of primary stem or root

cotyledon embryonic leaf

8

cross-pollination pollination between genetically different plants

cuticle plastic-like isolation layer

dehiscent fruits which open

dichotomous branching: when terminal bud always divides in two

double fertilization the process when two brothermale gametes fertilize two sis- ter female cells

elongation zone root: zone of expanding cells

embryo sac female gametophyte of flowering plants

endodermis the innermost layer of cortex

endophytic fungi fungi which grow inside plant body

endosperm1 haploid nutrition tissue originated from female gametophyte

endosperm2 triploid (sometimes diploid) nutrition tissue originated from second fertilization

epicotyl first internode of the stem

epidermis complex surface tissue

eustele vascular bundles in a ring

exodermis the outermost layer of cortex

fibers long and narrow sclerenchyma cells

fibrous root system no primary root visible

fiddleheads spiral tops of young fern leaves

floral units (FU) elements of generative system, fructifications

flower compact generative shoot with sterile, male and female zones, specifically in that order, other flower terms see in the separate glossary in the text

9

fronds leaves of ferns

fruit ripe floral unit (FU)

fusiform initials cambium cells which make vessel elements

general characters in leaf description, characters which are applicable only to the leaf as a whole

generative shoot system all generative shoots together

ground meristem primary meristem which makes cortex and pith

ground tissue same as parenchyma (see) but only applied for tissue

halophytes plants adapted to over-presence of NaCl

haustoria sucker roots of parasitic plants

heartwood non-functional part of wood

heliophytes plants adapted to full sun

hemiparasites photosynthetic plants, feeding partly on other plants

heterophylly situation when one plant has more than one leaf type

heterosporic with male and female spores

homoiohydric plants that save water

hydrophytes plants growing in water and frequently using water for the support

hygrophytes terrestrial or partly submerged plants adapted to the excess water

hypocotyl root/stem transitional place

idioblasts solitary cells dissimilar from surrounding cells

indehiscent fruits which do not open

indusia covers of groups of sporangia (sori)

10

inflorescence isolated generative shoot

integument extra cover of megasporangium

intercalary meristems which grow in two directions

internodes spaces between nodes

lateral meristem cambium, meristem appearing sideways

lateral veins smaller veins, typically branching out of the main vein (see)

leaf lateral photosynthetic organ of shoot with restricted growth

leaf primordia embryonic leaves

leaf scars marks of leaf petioles

leaf traces marks of leaf vascular bundles

lenticels “openings” in bark allowing for gas exchange

leptosporangia sporangia with 1-celled wall

main vein central, most visible vascular bundle of leaf (midrib)

marginal meristems which are located on margins

maturation zone root: oldest part of root

megaphyllous with leaves originated from joint branches

megasporangia female sporangia

megaspore female spore

megasporophylls modified leaves with attached megasporangia

meristems sites of cell division

merosity multiple of flower parts numbers

11

mesophyll photosynthetic parenchyma of leaf

mesophytes plants adapted to the average water

microspores male spores

microsporgangia male sporangia

monilophytes all Pteridophyta except lycophytes

monopodial branching: when terminal bud continues to grow every year

morphology visible, external structure

multiple fruit fruit originated from many pistils

mycoparasites plants feeding on soil fungi

mycorrhiza roots symbiotic with fungi

nodes place where leaves are attached

nucellus wall of megasporangium

ocrea part of the leaf which goes upwards along the stem

opposite leaf arrangement: two leaves per node

organ union of different tissues which have common function(s) and origin

orthostychy virtual line which goes trough similarly located leaves

orthotropic growth: vertical

ovule seed plants: megasporangium with integument

oxylophytes plants adapted to acidic substrates

palisade mesophyll mesophyll of elongated, tightly packed cells

parcellate reproduce vegetatively with easily rooted body parts

12

parenchyma tissue or cell type of spherical, roughly connected living cells

perforations openings

pericarp most of fruit tissue

pericycle parenchyma layer just outside of vascular tissues

periderm secondary dermal tissue

perisperm nutrition tissue originated from nucellus (see)

peristome mosses: attachment to moss sporangium, helps to distribute spores

petrophytes plants adapted to grow on rocky substrates

phellem external layer of periderm, cork

phelloderm internal layer of periderm

phellogen cork cambium, lateral meristem making periderm

phloem vascular tissue transporting sugars

phyllode leaf-like petioles

phyllotaxis leaf arrangement

pistil cupule, additional cover of ovules

pit structure connecting tracheids

pith central layer of primary stem or root

plagiotropic growth: horizontal

plants are not animals!

plants1 all photosynthetic organisms

plants2 kingdom Vegetabilia

13

pneumatophores air-catching heliotropic roots

poikilohydric plants that do not save water

pollen sac seed plants: microsporangium

pollen tube fungus-like cell which brings spermatia (see) to egg

pollination transfer of male gametophytes (pollen grains) from microsporangia (pollen sacs) to megasporangia (ovules) or cupules (pistils)

prickles modified, prickly stem surface growths

primary meristems intermediate tissues which start out of apical meristems and make primary tissues

primary root originates from embryo root

primary stem stem with primary tissues only

primary tissues tissues originated from RAM or SAM (optionally through inter- mediate meristems)

procambium intermediate meristem developing into cortex, pith and procam- bium, primary meristem which makes vascular tissues

protoderm primary meristem which produce epidermis or rhizodermis

protonema mosses: embryonic thread of cells

protostele central xylem surrounded with phloem

psammophytes plants adapted to grow on sandy substrates

quiescent center core part of root apical meristem

raceme basic monopodially branched inflorescence (Model I)

radial section: cross-section

RAM root apical meristem

14

ray initials cambium cells which make rays

rays stem: parenchyma cells arranged for horizontal transport

repetitive characters in leaf description, characters which are applicable to the leaf parts on each level of hierarchy

rheophytes water plants adapted to fast moving water

rhizodermis root epidermis, root hairs

rhizoid cells dead cells accumulating water apoplastically

rhizome underground horizontal shoot

ring porous wood: with large vessel elements mostly in early wood

root an axial organ of plant with geotropic growth

root cap protects root meristem

root nodules bulb-like structures which contain nitrogen-fixing bacteria

root pressure pressure force made solely by roots

SAM stem apical meristem

sapwood functional part of wood

schizocarp fruits which segregate into smaller indehiscent units

sciophytes plants adapted to shade

sclerenchyma dead supportive tissue

sclerophytes plants preventing water loss, they frequently employ sclerenchyma

secondary (lateral) roots originate from primary root (see)

secondary vascular tissues secondary phloem and secondary xylem

15

seed chimeric structurewithmother (seed coat), daughter (embryo) and endosperm genotypes

seed scales megasporophylls (see) of conifers

seta mosses: stalk of the sporogon (see)

sheath part of leaf which surrounds the stem

shoot plant body unipolar body: no root system, shoots only

sieve tube cells living cells which transport sugar

simple fruit fruit originated mostly from one pistil

simple leaf leaf with one level of hierarchy

simple tissues tissues with uniform cells

siphonogamy fertilization with the help of pollen tube

solenostele vascular bundles in “hollow” cylinder

sori clusters of sporangia

spermatium aflagellate, non-motile sperm cell (plural: spermatia)

spines reduced, prickly leaves

spiral leaf arrangement, or alternate leaf arrangement: one leaf per node

spongy mesophyll mesophyll of round, roughly packed cells

sporogon moss sporophyte

stele configuration of vascular tissues in stem or root

stem axial organ of shoot

stipules small attachments to the leaf; typically, located near the base of petiole

stolon aboveground horizontal shoot

16

stomata (stoma) pores which opened and closed by guard cells

succulents plants accumulate water

surface / volume law when body size grows, body surface grows slower then body volume (and weight)

sympodial branching: when terminal bud degrades every year

synangia adnate sporangia

tangential section when plane is tangent to surface

tap root system primary root well developed

tendrils organ modifications using for climbing

terminal characters in leaf description, characters which are applicable only to the leaf terminals (leaflets)

thallus flat, non-differentiated body

thorns prickly shoots

thyrsus basic sympodially branched inflorescence (Model II)

tissue is a union of cells which have common origin, function and similar mor- phology

tracheary elements water-transporting dead cells

tracheids tracheary elements without perforations (openings)

transverse section: longitudinal

tuber enlarged portion of rhizome

tyloses “stoppers” for tracheary elements made by parenchyma cells, vessel el- ement “stoppers”

vascular bundles “chords” made of xylem (inner) and phloem (outer) layers

17

vascular cylinder “hollow” cylinder made of xylem (inner) and phloem (outer) layers

vascular plants Pteridophyta + Spermatophyta

vascular tissues tissues which transport liquids

velamen absorption tissue made of dead cells

vessel members tracheary elements with preforations (openings)

wood secondary xylem, stem: everything deeper than vascular cambium

xerophytes plants adapted to the scarce water

xylem vascular tissue transporting water

18

Chapter 1

Introduction to the Introduction

1.1 Plants, Botany, and Kingdoms

Botany is the scientific study of plants and plant-like organisms. It helps us under- stand why plants are so vitally important to the world. Plants start the majority of food and energy chains, they provide us with oxygen, food and medicine.

Plants can be divided into two groups: plants1 andplants2. Plants1 contain all pho- tosynthetic organisms which use light, H2O, and CO2 to make organic compounds and O2. Plants1 are defined ecologically (based on their role in nature).

Some plants1 can be bacteria or even animals! One example of this a green slug, Elysia chlorotica (see Fig. 1.1). Green slugs collect chloroplasts from algae and use them for their entire life as food producers. Therefore, green slugs are both animals and plants1.

Plants2 are all organisms from Vegetabilia kingdom. Normally, plants2 are green organisms with a stem and leaves. We can define them also as multi-tissued, ter- restrial, and primarily photosynthetic eukaryotes. This definition is taxonomical (based on evolution).

It is possible for the organism to be plant2 but not plant1 (see Fig. 1.2). Those who fall into that category, are fully parasitic plants (mycoparasites like Pterospora, root parasites like Hydnora, stem parasites like Cuscuta, and internal parasites like Pi- lostyles) which do not practice photosynthesis but have tissues, terrestrial lifestyle and originated from photosynthetic ancestors.

19

Figure 1.1. Green slug Elysia chlorotica caprures chloroplasts from the algaVaucheria litorea.

Plants may be understood on several levels of organization: (from top to bottom) (a) ecosystems or taxa, (b) populations, (c) organisms, (d) organs, (e) tissues, (f) cells, (g) organelles, and (h) molecules (Fig. 1.3).

Botany is considered to be a “slice science” because it covers multiple levels of orga- nization.

1.1.1 Taxonomy

Taxonomy, systematics and classification are terms with similar meanings; they are all about the overwhelming diversity of living organisms, for there are more than 2,000,000 species (and 300,000 of them belong to plants2). Phylogenetics is a more fashionable term; it emphasizes the evolutionary history (phylogeny) of taxonomic groups (taxa).

This taxonomic organization is hierarchical. Most scientists accept sevenmain levels of taxonomy (ranks): the highest is kingdom, followed by phylum, class, order, family, genus, and lastly, species.

* * *

20

Plants1

Plants2

green slug, cyanobacteria, algae

melon, oak, cactus

full parasites

Figure 1.2. Plants1 and plants2.

The highest rank, kingdoms are easy to understand as the pyramid of life (Fig. 1.4) which is divided into four levels—kingdoms. At the bottom is Monera, which con- sists of prokaryotes (Bacteria and Archaea). This is the first level of life: Monera have simplest cells without nucleus. The next level is Protista. These are eukary- otes (nuclear cells) without tissues; some examples are algae and fungi. The final level consists of two groups: Vegetabilia and Animalia. They both have tissues but have obtained them for completely different purposes. Animals have tissues to hunt and digest, while plants have tissues mainly to survive on land. Viri which are mentioned sideways, are not living things but merely pieces of DNA or RNA which “went astray” out of cells of living organisms of all four kingdoms. Despite of being non-living, viruses are capable of evolution.

Plants2 (kingdom Vegetabilia) contain more than 300,000 species and divided in multiple subgroups (Fig. 5.1).

21

molecules

cells

organisms

ecosystems

Botany Mycology Microbiology

Entomology

Molecular biology

Cytology

Physiolology

Ecology plants fungi

insects

birds mammals

bacteria

. . .

. . .

. . .

. . .

Figure 1.3. Layered pie of biology: levels of organization (left), taxonomic groups (top), “slice” sciences (bottom) and “layer” sciences (right).

* * *

Ranks are used to compare taxonomic groups (taxa) from different major groups. No precise definitions are available for particular ranks, but it is believed that they are associated with the time of divergence (separation) between taxa. In addition to seven ranks mentioned above plant taxonomy uses intermediate ranks like subfam- ily, subclass or superorder—when taxonomic structure is too complicated.

Below is and example of names used for different ranks. Please note that names used for some ranks have standardized endings (underlined):

English Latin Example 1 Example 2

Kingdom Regnum Vegetabilia Animalia

Phylum Phylum Spermatophyta Chordata

Class Classis Angiospermae (Magnoliopsida) Mammalia

Order Ordo Liliales Primates

Family Familia Asparagaceae Hominidae

Genus Genus Chlorophytum Homo

Species Species Chlorophytum comosum (Thunb.) Jacq. Homo sapiens L.

22

Vegetabilia Animalia

Protista

Monera

tissues

nucleus

cell

Viri

Figure 1.4. Pyramid of Life.

It is frequent when one species has several geographical races without clear borders between them. The example might be the stinging nettle, Urtica dioica. In North America, many nettles have narrower leaves and are less stinging than in Eurasia. However, there are many intermediate forms between these races. To reflect this, taxonomists introduced two subspecies: in this case, Urtica diuica subsp. dioica (“Eurasian”) and U. dioica subsp. gracilis (“North American”). Another frequently used under-species category which is cultivar. Cultivars are frequently used in gar- dening. For example, many roses in cultivation belong to different cultivars of Rosa banksiae, and yellow roses are often Rosa banksiae cv. ‘Lutea’ where the last part of name is for the cultivar.

* * *

Names of species are binomials which consist of the name of genus and species epithet:

23

Name of species︷ ︸︸ ︷ Chlorophytum︸ ︷︷ ︸ Name of genus

comosum︸ ︷︷ ︸ Species epithet

(Thunb.)︸ ︷︷ ︸ First author

Jacq.︸ ︷︷ ︸ Second author

1862︸ ︷︷ ︸ Year of description

If one does not know the exact species, “sp.” shortcut is used instead of epithet, and “spp.” is used as a shortcut for multiple unknown species. It is required to use slanted font when one prints a name of species or genus. All scientific names are capitalized, but the second word in a species name (species epithet) always starts from lower case letter. It is a well-known fact that some species have a hybrid origin, and in these cases, botanists use a multiplication sign (×). For example, common plum (Prunus ×domestica) is a hybrid between blackthorn and cherry plum: Prunus spinosa × Prunus cerasifera.

The group of plants or animals must have one and only one name. Ideally, the name should be a stable ID for all occasions. But since biology is a “science of excep- tions”, some plant families are allowed to bear two names. As an example, legumes (Leguminosae) are frequently named “Fabaceae”, and grasses (Gramineae) have the second name “Poaceae”.

Throughout the long history of taxonomy, too many names were given to the same taxa. At themoment,wehave almost 20,000,000names to describe 2,000,000 species. These 18,000,000“excess names”are synonymswhich should not be used in science. To regulate the use of names, nomenclature codeswere created. These codes spec- ify, for example, the rule of priority: when two names are given for the same group, only earlier name is valid. Consequently, it is recommended to list the author and the year of description along with a name: “Homo sapiens L. 1758”, which means that founder of taxonomy, Carolus Linnaeus (“L.” shortcut) described this species in 1758.

Another important concept of nomenclature is the nomenclature type. Practically, this means that every species name must be associated with the physical museum specimen. In botany, these museums are collections of dried and pressed plants, called herbaria. Type specimens are of immense importance because there are no labels in nature, and only these specimens will “tell” about real plants or animals associated with particular names.

Names of taxa higher than species also have nomenclature types, but in these cases they are other names,not specimens. This examplemay clarify the use onnomencla- ture types. Initially, oleaster family (Elaeagnaceae) contained two genera, Elaeagnus (oleaster) and Hippophaë (sea-buckthorn). The second genus included Hippophaë rhamnoides (Siberian sea-buckthorn, type species) andHippophaë canadensis (North

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American plant). Thomas Nuttall decided to split sea-buckthorns in two genera. Since one of them contains Hippophaë rhamnoides, the type species, it should keep the name Hippophaë. The second genus can be named arbitrarily. Nuttall gave it name “Shepherdia”. As a result, the species which had name Hippohaë canadensis L., became Shepherdia canadensis (L.) Nutt.

Plant taxonomy is a science. That means that our understanding of plant groups will always change. It also means that there always are different competing opin- ions, the taxonomic hypotheses which describe plant diversity in different ways. As a result, some groups of plants could be accepted in a broad sense, including as many subgroups as possible. For example, there might be an opinion of Homo sapiens s.l. (sensu lato = wide sense) including not only contemporary humans but also Nean- derthal men. As a contrast, other opinions may accept groups in a strict sense, and Homo sapiens s.str. (sensu stricto = strict sense) includes only contemporary humans.

1.2 Styles of Life and Basic Chemistry

Life obtains energy in a few different ways: (1) from sunlight (phototrophy); (2) from chemical reactions with inorganic matter (lithotrophy); (3) from breaking or- ganic molecules into inorganic molecules, typically carbon dioxide and water (orga- notrophy). To make its body, living beings obtain building blocks either by (a) from the assimilation of carbon dioxide (autotrophy), or from other living beings (heterotrophy).

These ways combine in six lifestyles. For example, plants1 are by definition pho- toautotrophs. Most plants2 are also photoautotrophs, but there are exceptions: full parasites (see above). Carnivorous plants (like sundew, Drosera or the Venus flycatcher, Dionaea) are all photoautotrophs. They “eat” animals in order to obtain nitrogen and phosphorus, so the dead bodies serve not as food but as a fertilizer.

* * *

To understand life of plants, a basic knowledge of chemistry is needed. This in- cludes knowledge of atoms (and its components like protons, neutrons and elec- trons), atomic weight, isotopes, elements, the periodic table, chemical bonds (ionic, covalent, and hydrogen), valence, molecules, and molecular weight. For example, it is essential to know that protons have a charge of +1, neutrons have no charge, and electrons have a charge of –1. The atomic weight is equal to the weight of protons and neutrons. Isotopes have the same number of protons but different number of neutrons; some isotopes are unstable (radioactive).

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