1. Classification keys๏ƒ

1.1. Tabular keys๏ƒ

Dichotomous tabular classification keys can be created in LaTeX using the tabular environment.
vertebrates_key.png 
 1\documentclass[12pt, varwidth, border=5mm]{standalone}
 2\begin{document}
 3\begin{tabular}{l@{\hspace{1mm}}p{6cm}@{}r}
 41A. & Feathers present \dotfill &\dotfill birds \\
 51B. & Feathers absent \dotfill &\dotfill go to 2 \\
 62A. & Scales present \dotfill & \dotfill go to 3 \\
 72B. & No scales present \dotfill &\dotfill go to 4 \\
 83A. & Breathe with gills \dotfill &\dotfill fish \\
 93B. & Breathe with lungs \dotfill &\dotfill reptiles \\
104A. & Hair or fur present \dotfill &\dotfill mammals \\
114B. & Hair or fur absent \dotfill &\dotfill amphibians \\
12\end{tabular}
13\end{document}
LaTeX usage:

  • \documentclass[12pt, varwidth, border=5mm]{standalone}: This line specifies the document class and its options. The standalone class is used for creating a standalone document with a single page. The 12pt option sets the font size to 12 points. The varwidth option allows the content to determine the width of the page. The border=5mm option adds a 5mm border around the content.

  • \begin{tabular}{l@{\hspace{1mm}}p{6cm}@{}r}: This line begins a tabular environment, which is used to create a table. The argument {l@{\hspace{1mm}}p{6cm}@{}r} specifies the alignment and spacing of the columns. The l means that the first column is left-aligned. The @{\hspace{1mm}} syntax adds a 1mm space between the first and second columns. The p{6cm} means that the second column is a paragraph column with a fixed width of 6cm. The @{} syntax removes the space between the second and third columns. The r means that the third column is right-aligned.

  • 1A. & Feathers present \dotfill &\dotfill birds \\: This line represents a row in the table. The & symbol separates the columns and the \\ symbol marks the end of the row. The \dotfill command fills the space with dots.

arthropods_key.png 
 1\documentclass[12pt, varwidth, border=5mm]{standalone}
 2\begin{document}
 3\begin{tabular}{l@{\hspace{1mm}}r}
 41a. & Legs on every segment except head and last segment \dots \dotfill go to 2 \\
 51b. & Legs on thorax only \dots \dotfill go to 3 \\ 
 62a. & One pair of legs on each segment; flattened body \dots \dotfill Chilopoda \\
 72b. & Two pairs of legs on each segment; tubular body \dots \dotfill Diplopoda \\
 83a. & Three pairs of legs \dots \dotfill Insecta \\
 93b. & Four pairs of legs \dots \dotfill Arachnida \\
103c. & Five or more pairs of legs \dots \dotfill Crustacea \\
11\end{tabular}
12\end{document}
LaTeX usage:

  • \documentclass[12pt, varwidth, border=5mm]{standalone}: This line specifies the document class and its options. The standalone class is used for creating a standalone document with a single page. The 12pt option sets the font size to 12 points. The varwidth option allows the content to determine the width of the page. The border=5mm option adds a 5mm border around the content.

  • \begin{tabular}{l@{\hspace{1mm}}r}: This line begins a tabular environment, which is used to create a table. The argument {l@{\hspace{1mm}}r} specifies the alignment and spacing of the columns. The l means that the first column is left-aligned. The @{\hspace{1mm}} syntax adds a 1mm space between the first and second columns. The r means that the second column is right-aligned.

  • 1a. & Legs on every segment except head and last segment \dots \dotfill go to 2 \\: This line represents a row in the table. The & symbol separates the columns and the \\ symbol marks the end of the row. The \dots command produces an ellipsis (three dots). The \dotfill command fills the space with dots.

1.2. Branching keys๏ƒ

The forest package can be used to draw branching diagrams.
See docs at: https://ctan.org/pkg/forest?lang=en
vertebrates_branching_key_forked_edges.png 
 1\documentclass[border=10pt,multi,tikz]{standalone}
 2\usepackage[edges]{forest}
 3\usetikzlibrary{arrows.meta,shadows.blur}
 4\begin{document}
 5\begin{forest}
 6    forked edges,
 7    for tree={s sep=0.5cm,
 8        l sep=0.8cm,
 9        draw=blue!80!darkgray,
10        fill=blue!10!white,
11        rounded corners,
12        text width=(\textwidth)/5,
13        edge={-Latex},
14        font=\sffamily,
15        text centered,
16        blur shadow,
17    }
18    [Vertebrates
19        [1A \\Feathers present
20            [birds]
21        ]
22        [1B \\Feathers absent
23            [2A \\Scales present
24                [3A \\Breathe with gills
25                        [fish]
26                ]
27                [3B \\Breathe with lungs
28                        [reptiles]
29                ]
30            ]
31            [2B \\No scales present
32                [4A \\Hair or fur present
33                        [mammals]
34                ]
35                [4B \\Hair or fur absent
36                        [amphibians]
37                ]
38            ]
39        ]
40    ]
41
42\end{forest}
43\end{document}
arthropods_branching_key_forked_edges.png 
 1\documentclass[border=10pt,multi,tikz]{standalone}
 2\usepackage[edges]{forest}
 3\usetikzlibrary{arrows.meta,shadows.blur}
 4\begin{document}
 5\begin{forest}
 6    forked edges,
 7    for tree={s sep=0.5cm,
 8        l sep=0.8cm,
 9        draw=blue!80!darkgray,
10        fill=blue!10!white,
11        rounded corners,
12        text width=(\textwidth)/5,
13        edge={-Latex},
14        font=\sffamily,
15        text centered,
16        blur shadow,
17    }
18    [Arthropods
19        [1a. \\Legs on every segment except head and last segment
20            [2a. \\One pair of legs on each segment; flattened body
21                [Chilopoda]
22            ]
23            [2b. \\Two pairs of legs on each segment; tubular body
24                [Diplopoda]
25            ]
26        ]
27        [1b. \\Legs on thorax only
28            [3a. \\Three pairs of legs
29                [Insecta]
30            ]
31            [3b. \\Four pairs of legs
32                [Arachnida]
33            ]
34            [3c. \\Five or more pairs of legs
35                [Crustacea]
36            ]
37        ]
38    ] 
39\end{forest}
40\end{document}
Some of the LaTeX usage is below.

  • \usepackage[edges]{forest}: This line loads the forest package with the edges option. The forest package provides tools for creating tree diagrams, and the edges option enables additional features for customizing the appearance of edges in trees.

  • \usetikzlibrary{arrows.meta,shadows.blur}: This line loads two libraries from the tikz package: arrows.meta and shadows.blur. The arrows.meta library provides additional arrow tip styles that can be used when drawing edges in trees, and the shadows.blur library provides a blur shadow effect that can be applied to nodes in trees.

  • \begin{document}: This line marks the beginning of the document content. Everything between this line and the corresponding \end{document} line will be processed by the LaTeX compiler and included in the output document.

  • \begin{forest}: This line begins a forest environment, which is used to create a tree diagram.

  • forked edges,: This option specifies that the edges connecting the nodes in the tree should be forked.

  • for tree={...},: This option allows you to specify formatting options that apply to all nodes in the tree. The options specified within the for tree block will apply to all nodes in the tree.

    • s sep=0.5cm,: This option sets the distance between siblings (nodes that share the same parent) to 0.5 centimeters. This means that sibling nodes will be separated by a horizontal distance of 0.5 centimeters.

    • l sep=0.8cm,: This option sets the distance between levels (nodes that are one level apart in the tree hierarchy) to 0.8 centimeters. This means that nodes that are one level apart will be separated by a vertical distance of 0.8 centimeters.

    • draw=blue!80!darkgray,: This option sets the draw color for all nodes in the tree to a mixture of blue and dark gray.

    • fill=blue!10!white,: This option sets the fill color for all nodes in the tree to a mixture of blue and white.

    • rounded corners,: This option specifies that all nodes in the tree should have rounded corners.

    • text width=(\textwidth)/5,: This option sets the text width for all nodes in the tree. The text width is calculated based on the value of \textwidth and a scaling factor of 5.

    • edge={-Latex},: This option sets the style of the edges connecting the nodes in the tree. In this case, the edges are drawn with an arrowhead at the end using the -Latex arrow tip.

    • font=\sffamily,: This option sets the font for all text within the tree to be sans-serif.

    • text centered,: This option specifies that text within all nodes in the tree should be centered.

    • blur shadow,: This option adds a blurred shadow effect behind all nodes in the tree.