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Localized Keys and Predetermined Characteristics

Wednesday, March 16, 2016

The first step in using the FNA keys to determine the family of the specimen. The location of where that specimen was collected limits the possible families; this type of key localization is easily understood.

The key to taxa in a family can also be localized. Since some of the paths through the key will lead to taxa not in a given location, there must choices for some couplets that also do not lead to the location.
By tracing every possible path through the key for each taxa in the family (see Characters Sets and Paths), each couplet choice can be associated with a list of locations for taxa following that lead. Therefore, for a given location, the only allowed paths are those that either those through couplets with your location for either choice or through couplets with just your location for one of the choices; that is, if your location is not on the list of locations for a couplet choice, the only possible path is through the other choice.

The Alismataceae key is moderate sized, and the taxa in the family are widely, though not evenly, dispersed in North America. The following diagram for the key shows how it would be localized for taxa in Washington state. The couplet characters are not shown, but the couplet numbers are the same as those for the online key and for its subkeys.
It is generally not worthwhile to use locations lists with printed keys because lists are usually too long to print and too long for the user to look through the list. But they could be used with online keys and with keying apps for smartphones and tablets; the user would specify the location (or locations), and they would be presented with a localized key. As the user traverses the key, they would be told when their path passes a couplet that could be skipped, and the user would usually verify that their specimen has the characters of the choice in the path taken. For example, in the above example, before getting to couplet 2 (the first couplet where they need to make a choice), they would be asked whether their specimen has the characters in the 1+ couplet choice.

Creating good localized keys depends on accurate species location information. The webpage describing the regional keys for the Jepson eflora notes that, because of this, the key for larger area may need to be used to key out some species.

Predetermined Characters - Just like being able to localize a key, a key can be pre-processed for a given morphological character that is used to differentiate targets in the key; the only allowed paths are those that result in targets that have that desired character, simplifying key traversal.

For example, suppose you want to use the Ericaceae Kalmia key to key out a specimen that has alternate leaves.  Instead of using the key

1        Petals distinct nearly their entire lengths.                                                       7 buxifolia
+        Petals connate ca. 1/2 to nearly their entire lengths                                       (2)
2 (1)   Leaves opposite; inflorescences terminal, corymbiform racemes or umbels (3)
+        Leaves alternate (rarely opposite) or in whorls; inflorescences solitary
          flowers or fascicles, racemes, or panicles                                                      (5)
3 (2)   Midribs of leaf blades with purple, clavate trichomes; seeds 1.5-2.2 mm.     6 polifolia
+        Midribs of leaf blades without trichomes; seeds 0.5-1.4 mm                           (4)
4 (3)   Capsules 5-locular; petals 7-9 mm, shallowly cleft; stamens 10.                   5 microphylla
+        Capsules 2-3-locular; petals 3-5 mm, cleft ca. 1/2 their lengths; stamens 5. 8 procumbens
5 (2)   Leaves usually in whorls of 3 (rarely alternate or opposite)                           2 angustifolia
+        Leaves alternate or seemingly whorled                                                           (6)
6 (5)   Leaves deciduous; petals white with red band adaxially.                               3 cuneata
+        Leaves persistent; petals white to pink or red                                                (7)
7 (6)   Plants 8(-12) m; leaf blade surfaces glabrous adaxially (only midrib
           puberulent), 4-12 cm; inflorescences terminal panicles                                1 latifolia
+        Plants 0.6(-1.2) m; leaf blade surfaces usually hairy, 0.5-1.4 cm;
           inflorescences solitary flowers or, sometimes, fascicles or racemes,
           scattered along stem in leaf axils.                                                                 4 hirsuta

if this key had been pre-processed for alternate leaves, then you could use this smaller key

1        Petals distinct nearly their entire lengths.                                                       7 buxifolia
+        Petals connate ca. 1/2 to nearly their entire lengths                                       (2)
2 (1)   Leaves usually in whorls of 3 (rarely alternate or opposite)                           2 angustifolia
+        Leaves alternate or seemingly whorled                                                           (3)
3 (2)   Leaves deciduous; petals white with red band adaxially.                               3 cuneata
+        Leaves persistent; petals white to pink or red                                                 (4)
4 (3)   Plants 8(-12) m; leaf blade surfaces glabrous adaxially (only midrib
           puberulent), 4-12 cm; inflorescences terminal panicles                                1 latifolia
+        Plants 0.6(-1.2) m; leaf blade surfaces usually hairy, 0.5-1.4 cm;
           inflorescences solitary flowers or, sometimes, fascicles or racemes,
           scattered along stem in leaf axils.                                                                 4 hirsuta

For this method to be successful, work would be needed to parse the couplet leads, which can have ambiguous syntax, so it is not clear that use of predetermined characters would be cost effective.  However, it may offer an alternative to creating interactive multi-access keys while offering the major advantage of multi-access keys: most characters of a sample do not need to be examined in a predetermined order.

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