Characters Sets and Paths

As one makes binary choices of characters in a key, one creates a set of characters for the destination target and a path through the key. In listing the Characters Set (CS), it is more useful to reverse the order, so those characters chosen last are listed first because those are are most specific to the target.

For example, the CS for Boechera burkii is:

• Racemes usually unbranched; cauline leaves 18-28; ovules 64-80 per ovary; seeds 1.2-1.4 mm wide
• Biennials, without caudices; stems (2-)3-10 dm; cauline leaves 18-80
• Basal leaf blade surfaces glabrous or with simple trichomes only
• Cauline leaf blades not auriculate

However, the CS can be more complex. One reason is that there can be more than one CS for  a target when there are diverse characters leading to it. In the FNA keys, targets whose name is appended with "(in part)" in the key have more than one CS. Keys in this papers instead append CSn to the target, where n=1,2,…; that is, there are multiple characters sets, which are numbered.

Using Boechera repanda as an example, CS1 is:

• Basal leaf blades 10-25(-50) mm wide; petals 3.5-6 mm.
• Fruit valves pubescent

And CS2 is:

• Basal leaf blades 7-25(-50) mm wide, margins usually repand to dentate, rarely entire
• Fruits 2-5.5 mm wide, divaricate-ascending to erect, ± appressed to rachises
• Stems proximally with simple and/or branched trichomes usually less than 0.5 mm; ovules 8-52 per ovary
• Fruits not secund
• Fruits erect, ascending, or horizontal
• Fruit valves glabrous

If a target has multiple characters sets, then the targets may have the same general attributes, and only the more specific characters differ. For Boechera repanda the characters that are in common for CS1 and CS2 are:

• Plants usually sparsely to densely pubescent proximally (sometimes throughout)
• Styles 0.05-2 mm
• Basal leaf blade surfaces with at least some branched trichomes
• Cauline leaf blades not auriculate

From this point on as you read this paper,  make sure you can reproduce the diagrams given the source FNA keys. This will make sure you understand each concept as it is presented.

The following diagram for the Brassicaceae Boechera key shows how these characters-set lists relate to the type of diagram discussed in Couplets, Targets and Rows.

This diagram is easier to understand because it shows both couplet and row numbers and because it shows only the paths of interest through the key. From this, the list of characters for B. repanda CS1 can be found in rows 35 and 33, those for CS2 are in rows 73, 72, 70, 66, 48 and 34, and those in common for both CSs are in rows 26, 22, 10 and 1.

The paths for CS1 and CS2 merge at couplet 17; the choices for couplet 17 lead to either CS1 or CS2 of B. repanda. If there are multiple characters sets for a taxon, there will be one or more couplets that will be merge points where the taxon has the characters of both choices of the merge point couplet.

There are two other reasons that the characters set for the path through a key can be more complex. As discussed in Key Types and Subkeys, some taxa have keys with subkeys (as does Boechera); each of these subkeys, which may correspond to intermediate-rank targets, add a characters set or multiple characters sets.  Also, as shown in Multiple-Characters-Set Groups, a couplet can have multiple characters sets even if there is no subkey, although this is rare.

Using the above methods, it is possible to list every characters set for a family and to follow every possible path through the key.  For large families, with keys at each rank and possibly subkeys and alternate keys, that list can be long. However, as shown in Localized Keys and Predetermined Characteristics, following  every path allows one to create localized keys from the FNA key.