About the Keys
The keys
I have provided two types of taxonomic key. Dichotomous keys to genera, Pombalia, and Viola are complete and are the most reliable (although more tedious to use). The multi-access key is experimental and quite incomplete (and a few traits for particular taxa are probably not coded exactly correctly), but will get to a taxon or small group of taxa very quickly and might be fun to try first. Over the next few months, I hope to rework the multi-access key to be more complete and correct, so that with more traits and more atomizing of character states, it will be possible to get to exactly one taxon in most instances. One advantage of the multi-access key is that vegetative traits might get you closer to a single result or just a few taxa, while it will probably be impossible to narrow down possibilities much in the dichotomous keys (which emphasize chasmogamous flowering and cleistogamous fruiting traits).
The dichotomous keys are tabular rather than indented, to be more efficient with space. There is a key to Violaceae genera in our region, with hyperlinks to keys to species of Pombalia (a segregate genus from the old monolithic Hybanthus) and of Viola. There is a short key to the three species of Pombalia as well. For Viola, there is a key to four other keys representing four main groups of violets. In each key, each couplet is hyperlinked to others; you can go immediately to the next couplet by clicking on the number at the end of the current couplet, and you can also go back to the previous couplet by clicking on the number of the previous couplet in parentheses following the current couplet's number. At the top of each key is a link to take you back to the previous key.
I have erred on the side of more morphological traits rather than fewer in each couplet of the dichotomous keys. Hybrids are frequent to common in every group except for the yellow-flowered species, and having multiple traits available means that you have the opportunity to detect an unusual or hybrid plant if it doesn't exactly match the traits (and even discern the parentage). Some taxa appear quite different in cleistogamous fruit than in chasmogamous flower, and the fruits and seeds of acaulescent taxa in particular provide critical diagnostic features for confident identification of many of them, so having both flowering and fruiting traits is valuable. Even more importantly, we have presented what we know or think we know about violet diversity in our region, including several undescribed species we are studying and many "variants" about which we know almost nothing–except that they do not exactly match the published taxa we know. There are certainly more undescribed taxa out there awaiting discovery as well. By providing you with as much information in the keys and descriptions as possible, I have armed you with the tools to assist us in hunting for, studying and learning about this newly detected biological diversity.
I attempted to be very precise in using standard botanical terminology for all structures mentioned in the keys and descriptions (I drew the line, however, at using the term "trichome", which is technically what we should be calling a hair in plants). If some terms are unfamiliar to you, or you want to make sure that how I interpret the terms is what you think they mean, you might consult the dropdown menu of “Links”, the first of which leads to the New York Botanical Garden’s excellent glossary (sometimes illustrated) to botanical terminology. For a primer on violet morphology, go to “Morphology”.
Traits used in the keys and descriptions
If you are studying or preparing to collect plants in the field (an outstanding pursuit), don’t examine or collect only one or two individuals—they may be odd variants, hybrids, or a new taxon. Look closely at a dozen or two plants that appear to be part of a uniform population, and get a sense of their morphology first, before collecting them or using the key. It’s a good idea to take some cellphone pictures of habit of the plants, the leaves, and the flowers (in frontal and profile view) and any cleistogamous flowers, or cleistogamous fruits, as you study or collect the plants. Use a hand lens often, to check small features such as hairs. When you prepare labels, features that would not be obvious in dried pressed specimens should be added to the label information. Observe carefully these features, as they are diagnostic for various species.
•Nature, color and thickness of rhizome, presence of a stoloniform extension to the rhizome; and color and thickness of any stolons, whether they bear leaves, flowers and/or fruits along their length, and whether they terminate in a plantlet.
•Stipules, whether free, or adnate partially or mostly to their petioles; and their texture, shape and margins.
•Orientation of the leaves, and the relative position of the flowers to the leaves in acaulescent species.
•Color and indument of the petioles, and of upper and lower surfaces of the leaf blades including any purple flush or tinge to the lower surface (use a handlens to see any small or minute appressed hairs on the upper surface).
•Relative thickness of the leaf blades, shape of the largest leaf blades, whether the inner edges of the basal lobes meet or overlap in life as in a few unlobed-leaved species (NOTE: the leaf blades on very early blooming individuals may not have expanded sufficiently to express characteristics of the species in mid- to late chasmogamous flower, so check multiple individuals for leaf traits).
•Nature of the leaf dissection in violets with lobed or divided leaves, whether all leaf blades are divided or if some (especially the smallest/earliest in the season and latest in the season) are unlobed; and whether division is pedate (the terminal primary division remaining undivided), ternate (the terminal and lateral primary divisions are once-divided), or biternate, triternate or tetraternate.
•Color and indument of the peduncle, and the position of the bracts (relevant in separating V. epipsila from V. palustris.
•Color and indument of the calyx, and shape of the sepals and auricles (use a handlens to observe cilia).
•Color of the corolla including the general ground color, the color nearest the throat (whether a darker flush, or presence of any dense eyespot formed by "bleeding" and coalescence of nectar-guidelines), and the color of the throat.
•Shape of the petals, and whether their apex is emarginate or retuse.
•Presence and density of beards (tufts of hairs) on the lateral petals or spurred petal, and the shape of the hairs on the lateral petals (use a handlens or dissecting microscope).
•Relative exsertion of the stigma and orange stamen connective scales (while most species have these deeply inserted and scarcely or not at all visible, a few species have them prominently exserted and visible in life.
•Orientation of the cleistogamous flower/fruit peduncle (the initial peduncle orientation in flower changes in fruit in some species).
•Color, indument and shape of the cleistogamous capsule; be certain that you are examining a cleistogamous rather than chasmogamous capsule (see "Details about certain traits used in the key", below), as the two types differ substantially in morphology in some species.
•Size, shape and color pattern of mature seeds from naturally dehisced capsules (use a handlens or dissecting microscope).
Details about certain traits used in the keys
Length in leaf blade length:width ratios refers to the length of a flattened blade from the apex to the base of the midvein at the petiole summit for blades with tapering or rounded to truncate bases, or beyond the petiole summit to the middle of an imaginary line drawn between the lowermost points of the basal lobes in a cordate blade. Violets of the Acaulescent Blue group (sect. Nosphinium, subsect. Boreali-Americanae) belong to one of three broad groups: homophyllous uncut-leaved (all leaves unlobed), homophyllous cut-leaved (all leaves on a plant are lobed or dissected), or heterophyllous (earliest leaves just after winter and latest leaves in fall are unlobed, leaves produced during chasmogamous flower and through mid-cleistogamous fruit are lobed or dissected). Lobed or dissected leaf blades may be palmately (more correctly, ternately), biternately, triternately or even tetraternately divided, with something approximating the expected resulting number of ultimate lobes or a few less; or they may be pedately divided, which involves the terminal primary division remaining unlobed while the lateral primary divisions are once- or sometimes twice-divided, giving a “birdfoot” appearance to the leaf. Leaf shape and lobing can change substantially or even dramatically on many species from spring chasmogamous flower to summer cleistogamous fruit, such that the plants from the two seasons may not appear to be the same; going back to the same population to study and collect them during both seasons is edifying (bringing flowering plants home and potting them up to study through summer and fall is even more efficient).
Nectarguides and color changes near the throat are ignored in references to chasmogamous corolla unless the nectarguide color or color change distinguishes species (for instance, the eyespot around the throat in V. communis f. priceana, V. cucullata, V. "floridana peninsular Florida”, and V. rostrata).
Chasmogamous capsules can be differentiated easily from cleistogamous capsules, as the former terminate in an elongate straight style, whereas cleistogamous capsules terminate in a small tightly curled style.
Ecological diversity supports taxonomic diversity in the Violaceae and other plant families. In the case of Viola in particular, it is not rare to find 10 or more species inhabiting a single topographically and ecologically heterogeneous natural area of modest size. Certain species may occupy a very restricted area of a given site, influenced by topographic position and substrate. Take note of the general ecology of the site as you study and collect violets: open or wooded; wet, moist or dry substrate; plant indicators that my give away the general acidity or alkalinity of the substrate, or exposures of bedrock.
Minute hairs in species with puberulent foliage are easiest to see by holding up the structure to the light and observing with a handlens; even with the naked eye the hairs will "glisten" in the backlighting and be more obvious.