I. An Introduction to Learning about Plants

Learning Objectives:

Define two things almost all plants have in common
Explain how evolution through natural selection led to diversification of life
List the hierarchy in taxonomy
Differentiate and explain the two terms of the binomial name
Compare and Contract the four frequently occurring subspecific taxa
Compare & contrast taxonomy, nomenclature, and systematics
Explain pedagogical tools for assessing and understanding one's learning

1. What Are Plants?

Introduction

When taking a walk outside, you might feel the cool shade of a tree, the cushiness of grass beneath your feet, or the smell of blossoms wafting in the wind. These are a few of the ways one might experience plants in a neighborhood or city. Have you taken the time to think about all the different types of plants? Go for a short walk and try to determine as many unique kinds of plants as possible. How many did you find? What colors did you encounter? What are some characteristics that they all have in common? Modern scientists will agree there are two things that almost all plants have in common: 1. Being multicellular (i.e. made of more than one cell). 2. Being photosynthetic (i.e. converting light energy called photons into chemical energy stored as sugars).

Origins of Diversity of Plants

It is often good to begin at the beginning. From cosmological data, we know our universe came to be 13.8 billion years ago. 4.5 billion years ago, our planet earth is formed. 4.0 billion years ago the first self-replicating molecules are believed to have existed. 3.7 billion years ago, what we consider life on earth began.

These first initial life-forms were relatively simple, single celled organisms living in the most extreme environments on earth. Subjected to different environmental conditions as they spread across earth, life evolved different characteristics to suit that environment and out-compete other organisms. Evolution is the process in which characteristics change over many generations being driven by natural selection. This is a slow, gradual change over time. Evolution is driven by a phenomenon called Natural Selection, in which the organisms whose characteristics are best suited to survive in an environment are likely to reproduce in that environment. Natural selection relies on inheritance (characteristics can be passed from parent to offspring), variation (different characteristics in a reproducing group), and competition with adaptation (the organisms in a reproducing group have to compete for non-abundant resources with those who outcompete others will have a greater probability of reproducing. This makes those offspring better suited or adapted to that particular environment.) To put it simply, the organism that is able to survive and reproduce the most will pass on its characteristics the most, and those that do not survive will not be able to reproduce and pass on its characteristics. For many people, it is easy to understand natural selection as it fundamentally operates on the scale of one generation. Evolution is often harder to conceptualize as it occurs on the scale of many generations. To summarize, evolution driven by natural selection is the process by which all diversity on earth arose over billions of years.

An example of natural selection can be seen within a population of moths. There is a population of moths that range in color from black to gray to brown and live on brown tree bark. The black and gray moths on the brown tree bark are readily seen by birds and get eaten. The brown moths on the brown tree bark are not readily seen; therefore they survive and reproduce. The characteristic of being brown colored can be passed from one generation of moths to the next generation of moths; thereby continuing the brown moths on that brown tree bark. On a nearby tree the bark is gray, so the gray moths survive and reproduce while the black and brown moths are devoured. In this example, there are two distinct groups of moths: the brown group and the gray group. Natural selection leads to the specification of moth characteristics in certain environments where those characteristics are advantageous for survival. When this occurs over many generations with gradual changes, the two groups of moths can develop significantly different characteristics to the point that they are unable to reproduce with each other.

2. How Do We Group & Name Plants?

Taxonomy, Nomenclature & Systematics

With such tremendous diversity, there is a desire to group and classify organisms. In our euro-centric history of science, Aristotle (384 BCE- 322BCE) is recorded as making a distinction between things that move calling them animals, and things that do not move calling them plants. This early dichotomy considered fungi, bacteria, protists and archea all plants. Today, scientists recognize distinctions between these groups and divide them into their own distinct sections. The science of organizing, classifying and naming organisms within a hierarchical structure is known as taxonomy. Taxonomists (the scientists of taxonomy) use a variety of characteristics from morphology (shape) to genetics to group and classify life. These groups are called taxa (the singular form is taxon). An example of a taxon is the taxon of plants, which means the group of all the plants. These taxa can encompass other taxa; thereby creating the hierarchical ranking of taxonomy. For example the taxon of all plants can include the taxa of plants that make flowers and those that make cones. The taxon of plants that make flowers can be split into all the taxa of types of flowers. This taxonomic ranking system allows us to better group and organize life.

Today, there are seven primary ranking levels. From largest to smallest these are kingdom, phylum, class, order, family, genus, species. These are a hierarchy such that multiple phylum will be within one kingdom, multiple classes within a phylum, multiple orders within a class, and so forth. In plant taxonomy, the three lowest primary ranking levels are most relevant: family, genus, and species. There are secondary ranking levels between the seven primary ranking levels with the three more often discussed being subfamily, subgenus, and subspecies. As discussed, taxonomy focuses on grouping, ranking, and organizing, but how do we develop names for these groups?

Each language and culture can have its own name for an organism. For example, one type of fern is called kupukupu in Hawaiian, but also called fish-bone fern in English. These are examples of the colloquial name or common name of the organism and are usually not the same across languages or cultures. This causes a need for a universal and standardized name in order to promote clear communication across languages and cultures to be established. The naming of life is referred to as nomenclature, with naming of plants referred to as botanical nomenclature. In the 1500s in Medieval Europe, Latin became the language of European science with an objective to unify science across countries. In 1623, Swiss Botanist Gaspard Bauhin published his classification of plants titled Pinax Theatre Botanici in which he provided two Latin names to many plants. Bauhin's classifications were mainly by utility including a groups for shrubs, trees, spices, and legumes. His work is one of the earlier accounts of binomial nomenclature, or naming using two terms. This meant that Bauhin named a plant by two terms similar to how many people have a first and last name.
In the History of Science, an individual (typically a European man) is glorified or noted as the "father" or "mother" of something. While it is understood that in nearly all instances no one person is solely responsible for the beginning or invention of something, our histories tend towards glorifying an individual as it is easier for story telling and provides a heroic figure. Carolus Linneaus (aka Carl Linneaus or Carl von Linne) is that individual for botanical nomenclature and modern taxonomy. His 1763 publication Species Plantarum is considered the foundational text for botanical binomial nomenclature with many of his original names being used today. After the binomial name, if there is a capitalized L., this indicates that this is the original nomenclature proposed by Linneaus.

Breaking Down the Binomial Name:

Just as Linneaus had hundreds of years ago, scientists today use the binomial name, also known as the scientific name, to refer to plants. The binomial name is comprised of the genus name and the species name. For example, the Mediterranean Cypress, the emblematic, columnar tree of Middle Eastern and Mediterranean iconography, has the binomial name Cupressus sempervirens. The genus name can be likened to the last name of a person. The genus Cupressus is the taxon of cypress plants. Genus name is always written with a capital first letter and italicized or underlined when handwritten.

The second term in the binomial name is the species name, which could be likened to the first name of a person. In the Mediterranean Cypress example, this would be the name sempervirens. Like the genus name, the species name is to be italicized or underlined if handwritten, but should be lowercase. Keeping with Medieval European science, these taxa names are in Latin. The Latin taxa name can be a descriptor of the plant, a location, or a person's name. With Cupressus sempervirens, Cupressus is the Latinized version of the original Greek name kyparissos, while sempervirens literally translates from Latin as "always green". Another plant in the cypress genus is the Moroccan Cypress known as Cupressus atlantica. The species term, also known as specific epithet, is atlantica, in reference to the Atlantic Ocean. As one learns more scientific names, learning a bit of Latin or Greek along he way could help with identification or recollection. (You will find that many Latin names are "turned into Latin" from the initial Greek names. This process is called Latinization.)

One final example of a descriptive binomial name is with the Texas chaparral bush Leucophyllum frutescens. This drought tolerant plant bears white, fuzzy leaves and usually maintains a bush or shrub-like form. Latinized to leuco from the Greek word leuko meaning "white" and Latinized to phyllum from the Greek word phyllon meaning "leaf", the generic name (another way to say genus name) literally means "white leaf". This is a bit on the nose, but descriptive. The specific epithet frutescens is from the Latin frutex meaning "shrub" and the suffix -esco meaning "to become"; hence meaning "to become a shrub". The scientific name can be roughly translated to "white leaf plant that becomes shrub-like."Of course there are plenty of plants that could fit this description, but understanding scientific name meanings can help with recalling names.

Leucophyllum frutescens translates from Latin to "White leaf that becomes shrub-like"
Photo by Matthew Gaston

Being More Specific: Subspecific Taxa

Common in landscapes are plant species with distinct characteristics from other members of that species; thereby warranting another taxa name beneath the species name. This subgroup (generally referred to as an intraspecific rank or subspecific taxon) could be a subspecies name, a variety name, cultivar name, or form name. When a third name is present, this makes the scientific name a trinomial name (because there are three terms). In summary, these four subspecific names add another taxonomic level for specificity. Below are more in-depth descriptions of the four most frequently occurring subspecific taxa:

Subspecies: the taxonomic rank below species usually used to signify a geographically isolated group usually differing morphologically from other members of the species. There must be at least two subspecies in the species or this taxa is irrelevant. In plant science, the abbreviation ssp. or subsp. is written before the subspecies name. The subspecies name is to be written in lowercase letter and italicized.

Example: Ipomoea pes-caprae ssp. brasiliensis

Ipomoea: Generic Name

pes-caprae: Specific Epithet

brasiliensis: Subspecies Name

Variety: the botanical taxonomic rank below species and subspecies usually used to signify a group of plants within the same geographic region as other members of the species, but with distinct characteristics from other members of the species. Because the varieties are found within the same geographic region, intergradation (the process in which two distinct populations reproduce and share characteristics between the two) is not uncommon. The abbreviate var. is written before the variety name. The variety name is to be written in lowercase and italicized.

Example: Tabebuia heterophylla var. alba

Tabebuia: Generic Name

heterophylla: Specific Epithet

alba: Variety Name

Cultivar: the botanical taxonomic rank below species that arose as a result of cultivation, or by direct manipulation by the cultivator. Short for 'cultivated variety', cultivars are usually the most frequent subspecific taxon in the standard tropical landscape. More specifically, a cultivar is an assemblage of plants that (a) has been selected for a particular character or combination of characters, (b) is distinct, uniform, and stable in those characters, and (c) when propagated by means appropriate, retains those characters. (Brickell, 2009) Cultivar names are regulated by and should be in accordance with the International Code of Nomenclature for Cultivated Plants (ICNCP). Cultivar names (also called cultivar epithets) are to be in any language except Latin, capitalized, written in print, and flanked on both sides by a single apostrophe (').

Example: Dracaena marginata 'Tricolor'

Dracaena: Generic Name

marginata: Specific Epithet

'Tricolor': Cultivar Epithet

Form: the botanical taxonomic below that of species, subspecies, and variety used to denote a a group with noteworthy morphological differences. Plants with the same form (also known as forma) name do not necessarily need to be closely related. This subspecific taxon could be applied excessively based on morphological differences in species, but infrequently has pragmatic utility; thereby making this subspecific taxon the least common of the four mentioned here. The form name is to be written in lowercase and italicized with the word forma or abbreviation f. before it. (The author believes form is archaic)

Example: Echinocactus wislizeni f. albispinus (This is an unaccepted scientific name for Ferocactus wislizeni)

Echinocactus: Generic Name

wislizeni: Specific Epithet

albispinus: Form Name

Understanding Relationships: Systematics

When discussing the scientific name, the generic name was likened to a person's last name. In most cases the plants within the same genus are closely related compared to a plant of a different genus. We say that these plants within the genus shared a recent common ancestor. This is similar to saying 'my cousins and I share the same grandparents'. The difference in the analogy is that plant evolution takes place over many generations instead of the two in the example. The study of organisms and their relationships to each other including evolutionary ancestry and evolutionary environmental adaptations is called systematics. Systematics uses evolutionary trees to model the connections and relationships of life. Systematics is introduced here in the introduction as it is often used interchangeably with taxonomy and nomenclature, but these are different. Taxonomy focuses on developing a hierarchy with groups, nomenclature focuses on naming, and systematics focuses on evolutionary relationship. Together, these fields help us classify, group, name, and understand relationships between life.

Changing Names for Changing Knowledge: Synonyms

In the early days of nomenclature and taxonomy, taxa were formed based primarily on morphology, especially flower morphology. While morphology does allow for pretty decent grouping and naming, the 'gold standard' is grouping based on genetic sequence. As scientists evaluate the genetic sequences of plants in conjunction with morphological characteristics, the taxa and names of the past might be inconsistent with the new findings. In these instances, a new taxon could be created or two taxa could be merged, and in these cases there will be a name change. This means that on top of one plant having twelve common names, it could also have twenty scientific names, but only one these is the accepted scientific name. The previous and currently unofficial scientific names are referred to as unaccepted scientific names or synonyms. For example, the cactus Ferocactus wislizeni has 18 synonyms, one of which being Echinocactus wislizeni f. albispinus. Note the generic name change, while the specific epithet remained the same, while dropping the form name. When a plant scientific name changes, the landscape and horticulture industries often will use continue using the synonym as it is familiar and everyone knows it by that synonym. A prime example of this is with the popular houseplant plant called sansevieria. In 2017, this plant was reclassified into the genus Dracaena to better represent its evolutionary history with other generic members, but most people still use the pre-2017 genus Sansevieria. This is an example of where knowing the synonym is actually more important than the accepted scientific name. Other examples of this include Golden Pothos (Epipremnum aureum) and Munriodendron (Polyscias racemosa) where the most popular English common name is the old generic name.

Shared Characteristics, Non-Vascular Plants, and Vascular Plants

Now that we have discussed how natural selection gives rise to diversity and how people have developed methods for naming, organizing, and understanding relationships, it is understood that there are a lot of different types of plants. One way of organizing plants is by shared characteristics, with the general assumption that the more shared characteristics, the greater probability that these plants are closely related and derive from a common ancestor compared to those without the shared characteristics. This group of organisms with a shared common ancestor is called a clade. While clades might not necessarily fall into a taxonomic rank like phylum, class, or order, they should represent shared evolutionary history- they are useful ways of grouping and thinking about plants.

One chiefly important feature of plants is the ability to move water and nutrients. The tissue (group of cells) that moves water and nutrients over long distances is called vasculature, which can be simplified to the idea of fortified plumbing. From here we can divide plants into two clades: 1) Vascular Plants, 2) Non-Vascular Plants.

Non-vascular plants do not have methods for moving water and nutrients over long distances, so these plants are often small and grow in wet areas. Examples of non-vascular plants are the mosses (of the phylum Bryophyta), liverworts (of the phylum Marchantiophyta), and the hornworts (of the phylum Anthocerotophyta). Some folks consider algae to be plants, in which case, algae are non-vascular plants.

Vascular plants are plants that have vasculature. Examples of vascular plants include the clade of spore-bearing plants (comprised of the extant phyla Polypodiaphyta and Lycopodiophyta), the clade of naked seed-bearing plants (comprised of the extant phyla Pinophyta, Cycadophyta, Ginkgophyta, and Gnetophyta), and the clade of fruit-bearing plants (i.e. the clade Magnoliaphyta). This course will focus on vascular plants as they are the dominant clade in the landscape.

3. Knowing, Understanding, & Assessing Your Learning

What do you know and how do you know that you know? Perhaps we know the name of a plant, but what do we really know about that plant? One of the trappings of plant identification is the primary focus is to recognize the plant to the genus, species, or subspecies level, but merely knowing the name does not indicate extensive knowledge on that plant. Where is it from? What kind of soil does it prefer? What lighting conditions? Does it produce interesting chemical compounds? These are all questions whose answers are arguably more important than merely memorizing a name. Names are necessary for clear communication, but they are not necessarily indicative of further understanding. Famous 20th century physicist Richard Feynman provided the following explanation to an interviewing when sitting by a forest: "See that bird? It's a brown-throated thrush, but in Germany it's called a halzenfugel, and in Chinese they call it a chung ling and even if you know the names for it, you still know nothing about the bird. You only know something about people; what they call the bird. Now, that thrush sings, and teaches it's young to fly, and flies so many miles away during the summer across the country, and nobody knows how it finds its way." For plant identification, this is a reminder that memorizing a name is not the end of one's learning. Indeed identifying and recalling the name is important, but there is much more that can be learned. I find that a brief look into meta-learning allows one to think more critically about how one learns and improve one's ability to learning.

Learning Objectives

In any undertaking, establishing clear, actionable, measurable, feasible goals can direct one's actions. Learning is no different; therefore, it is important to establish learning objectives (also called education objectives). These learning objects should always be tangible and measurable, such that one can clearly identify if it is completed.

An example of a good learning objective for this lesson is as follows:

Compare and contrast taxonomy, nomenclature, and systematics

An example of a poor learning objective for this lesson is as follows:

Understand taxonomy, nomenclature, and systematics

Note how the first learning objective includes a specific action to demonstrate one's understanding of taxonomy, nomenclature, and systematics. The second learning objective is vague and not specific as to what action needs to be accomplished to demonstrate learning objective completion. Selecting the appropriate action verbs depends on the complexity level of objective. Bloom's Taxonomy of Education Objectives provides a framework for thinking about learning objective complexity and appropriate action verbs for each level.

Bloom's Taxonomy of Education Objectives

In 1956, psychologist Benjamin Bloom released Taxonomy of Educational Objectives, which provided a rubric or hierarchy of educational objectives ordered by complexity. "Bloom's Taxonomy" (as it is usually called) became a tool for many educators and learners to understand the levels of complexity of learning. Revised in 2001, Bloom's Taxonomy is comprised of six levels from least complex to most complex: Remembering, Understanding, Applying, Analyzing, Evaluating, and Creating. By understanding Bloom's Taxonomy, learners can understand better to assess their own learning with the target goal to master the lowest level of complexity (Remembering) and learn our way up to the highest level of complexity (Creating). It is important to note that no one level is more important than other levels, rather they require different degrees of comprehension and cognition to be completed. A good starting point for learning is with remembering and understanding and developing skills to later evaluate and create. Bloom's Taxonomy is particularly useful in developing educational strategies for developing skills.

Remembering: recalling specific names, facts, dates, ideas, or concepts.

Action Verbs: recall, memorize, define, repeat, state, list, label, recite

Example: There are two general forms of Mediterranean cypress (Cupressus sempervirens): a columnar form and a spreading form.

Understanding: displaying an understanding of facts, ideas, or concepts through the ability to summarize, interpret, compare, and contrast.

Action Verbs: summarize, explain, restate, paraphrase, interpret, give examples, compare, contrast

Example: Compare and contrast the two general forms of Mediterranean cypress (Cupressus sempervirens)

Applying: using gained knowledge to solve a problem in a specific situation or circumstance.

Action Verbs: show, produce, solve, apply, use, sketch, demonstrate, implement

Example: Apply your knowledge of Mediterranean cypress (Cupressus sempervirens) to explain which form would be a better shade-providing tree.

Analyzing: deconstructing into component parts to investigate components or organization.

Action Verbs: examine, differentiate, distinguish, categorize, divide, relate, test

Example: Distinguish between the landscape applications of the two forms of Mediterranean cypress (Cupressus sempervirens).

Evaluating: judging based on presented criteria or references

Action Verbs: judge, critique, support, defend, argue, evaluate, recommend, value

Example: Recommend appropriate uses of each form of Mediterranean cypress (Cupressus sempervirens) in the landscape and support your recommendations using three references.

Creating: developing, constructing, or building ideas, concepts, organizations, or revisions using learned facts, ideas, or concepts.

Action Verbs: make, build, construct, compose, design, hypothesize, develop, organize, plan, produce

Example: Design a landscape plan that properly incorporates the two forms of Mediterranean cypress (Cupressus sempervirens).

An overview of 2001 Taxonomy of Educational Objectives Revision is available here.

Assessing One's Learning: How Do I Know That I Know?

As you embark on a new learning adventure, it can be helpful to have the right tools to complete the adventure to your satisfaction. When learning, it is important to assess oneself to see what one has truly learned. These assessments can give insight into what we have learned and what we need to continue learning. In pedagogy, there are two types of assessments: formative and summative. Formative assessments are the frequent checks along the adventure, while summative assessments are like the last challenge before completing the adventure. In the classroom formative assessments could take the form of casual discussions, quizzes, surveys, or journaling, while summative assessment would take the form of a final exam, final paper, final project, or final presentation. The formative assessments aim to provide the learner an opportunity to determine how much one has learned while still in the learning process, while the summative assessment is intended to assess all learning objectives across several or all levels of Bloom's Taxonomy at the end of the learning process. While this online mini-course does not have proper assessments, the learning objectives can be your formative assessments.

Learning Objectives:

Define two things almost all plants have in common
Explain how evolution through natural selection led to diversification of life
List the hierarchy in taxonomy
Differentiate and explain the two terms of the binomial name
Compare and Contract the four frequently occurring subspecific taxa
Compare & contrast taxonomy, nomenclature, and systematics
Explain pedagogical tools for assessing and understanding one's learning

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