TAXONOMIC CHARACTERS

Comments on specific morphological and anatomical features of taxonomic importance are

 given in the following paragraphs, while evaluations of phylogenetic polarizations of characters are related in the section on cladistics. A number of treatments describe the morphology of the mosses in detail; those of Flowers (1973a) and of Saito (1975a) include much up-to-date discussion and illustration of the morphology of the Pottiaceae.

Color

Emphasis is placed on natural coloration (see discussion of Mårtensson & Nilsson 1975) as a character only for those taxa in which color correlates with other, taxonomically important characters, e.g. Erythrophyllopsis (red leaves) or Scopelophila (blackish leaves). Even such genera with characteristically red or black leaves can be mimicked by placing a related but less colorful genus in KOH solution to develop leaves of a red coloration or in ferric chloride solution to create blackish leaves (cf. Field 1977). Thus, substrates that are highly alkaline or are associated with iron deposits may produce false color characters in certain taxa, just as characteristic coloration of other taxa may be suppressed in acid or iron-deficient habitats. As a rule, highly colored plant parts are yellow in acid solution and red in alkali, but this often varies per genus. A basic chemistry seems to permeate collections growing on calcareous rock, judging, for instance, from the strong bubbling of gas commonly produced from capsules of calciphiles placed in dilute HCl solution. One of the long-used characters of Barbula convoluta is the yellow seta. This seems to be a stable character, as the color becomes merely light orange in dilute KOH solution, quite different from the deep red evoked in, say, the setae of B. unguiculata. The peristomes of both species, however, show the same reactions to dilute HCl and KOH solutions, being light yellow in the first and deep red in the second. Changes in color can be expected, too, for observations of peristomes in lactophenol gel or Hoyer's solution mounting media (both acidic) or the highly alkaline KOH solution that might be used to help remove the operculum. For accuracy, color of plant parts should be used as a taxonomic character only when such parts are immersed in the acid or basic media standard for such observations.

The present taxonomic treatment emphasizes color responses of leaf laminal walls to two-percent KOH solution. These color reactions are usually either brick red or a bright yellow, occasionally orange, seldom negative (colorless, no change, or with the color of chlorophyll). Apparently (R. Mues, pers. comm.), the yellow and red reactions are characteristic of phenolic compounds—those compounds with only one or no hydroxyl groups giving a yellow color in KOH, while those with two or more closely associated hydroxyls will yield red. All other descriptions of coloration are given here as the natural state, and the general taxonomic value of these is not emphasized. Often, the yellowish green of chlorophyll masks somewhat the reaction of the cell walls to KOH (e.g. in the case of Chenia leptophylla, which at first glance appears light yellowish green in KOH under the dissecting microscope); when in doubt, the taxonomist should look at the lamina under high magnification to determine the actual color of the cell walls (which are actually bright purplish red in C. leptophylla).

The color reaction of the laminae to KOH solution is apparently unaffected by at least some chemical treatments involved in collection of mosses. Plants of Bryoerythrophyllum ferruginascens were boiled in 38% formaldehyde solution and also in 95% ethyl alcohol and, after rinsing, the laminae retained their ability to switch from red to yellow in dilute hydrochloric acid and back to red in two-percent KOH.