Dalea pringlei

Rupert C. Barneby

14. Dalea pringlei Gray

(Plates XXXVIII and XXXIX)

Perennial, herbaceous or in age weakly suffruticulose, glabrous up to the silky- pilosulous flower-spikes, variable in stature, the prominently angulate-ribbed, pale- green, rarely purplish, in age often pruinose-glaucescent, minutely and remotely punctate stems either several, assurgent or diffuse, and ± 2-10 dm tall, or 1-few, erect, virgate, and sometimes reaching 2.5 m, simple only when very short, commonly branched upward from the middle or at least distally, the spikes terminal to all branch- lets, the foliage green or subglaucescent, the leaflets smooth above, punctate beneath; stipular spurs 0.5-1.4 mm long; stipules narrowly subulate, rigid or even subspinu- lose in age, 0.5-2 mm long; intrapetiolular glands obsolete; post-petiolular glands minute, impressed; leaves 1.5-8 cm long, shortly but distinctly petioled, with narrowly margined, sparsely punctate rachis and few to many pairs (3-33, according to variety) of leaflets 1-15 mm long, variable in shape; peduncles 1-6 cm long; spikes narrowly ovoid becoming or from the first cylindroid, relatively loose, including bracts but without petals 8-12 mm diam, the villosulous axis becoming (1) 1.5-14 cm long; bracts persistent, subdimorphic, the lowest broadest, mostly ovate, the rest more narrowly ovate- to lance- or elliptic-acuminate, 2.5-5.5 mm long, always densely ciliolate and glabrous within, variably pubescent dorsally but in the distal half glandular, commonly fuscous or livid, sometimes green; calyx (3.5) 4.3-6.1 (6.5) mm long, densely silky-pilose externally, the tube 1.7-2.5 (2.7) mm long, its orifice subsymmetrical, the ribs prominent but slender, orange-brown, the membranous intervals charged with one row of 3-6 (7) small, honey-colored glands, the triangular-acuminate or shortly aristate, entire teeth commonly 2.4-4 (in var. oxyphyllidia only 1.4-2) mm long, plumose; petals most commonly bicolored with white to ochroleucous (but rubescent) sometimes lilac-tipped banner and epistemonous ones pink-purple or vivid magenta, the latter sometimes pale or white, these perched almost at or up to 1.2 mm below separation of the filaments; banner 3-5.1 mm long, the claw 1.7-3.4 mm, the deltate- cordate or rhombic-flabellate blade 1.2-2 mm long, 1.2-2.4 mm wide; wing and keel- petals similar but the inner pair sometimes a trifle shorter, wider, and more oblique, (1.8) 2-3.1 mm long, the claws 0.1-0.5 mm, the oblanceolate-obovate blades cuneate at base, 1.7-2.6 mm long, 0.8-1.5 mm wide; androecium 10-merous, 5.5-7 mm long, the filaments free for 2.2-3.2 mm, the connective gland-tipped, the yellow anthers 0.5-0.6 mm long; pod as in D. grayi, 2.5-3 mm long; seed (little known) 1.7-2.2 mm long.

From the time of their discovery and first description D. pringlei and D. grayi have been recognized as near kindred, and as their ranges of morphological variation have expanded along with knowledge of their narrowly overlapping ranges, it has become increasingly difficult to separate them in absolute terms. In Arizona, where they have been found close together even though properly belonging to different altitudinal strata in the foothills, D. pringlei being adapted to more xeric conditions that its relative, they can be told apart by the color of the epistemonous petals, always vivid purple in D. pringlei and white in D. grayi. Here also the calyx-teeth of D. grayi are substantially shorter in relation to the tube than those of D. pringlei. The mature spike of D. pringlei becomes moderately loose, so that flowers of pressed specimens tend to fall into two or three ranks and expose parts of the axis, which is concealed by crowded flowers in a comparable spike of D. grayi. In most cases the bracts of D. grayi are narrower than those of D. pringlei, 0.8-1.2 rather than 1.2-2 mm wide, but there is some overlapping in this character. In northern Mexico D. grayi becomes more variable and individual plants, although always white-flowered, may have relatively loose spikes, calyx-teeth (rarely) as long as the tube, or broad bracts; however I have not seen these characters together on one plant. Along the state line dividing southern Sonora from Chihuahua D. pringlei is represented by a series of giant forms with wandlike stems bearing long, sometimes relatively dense flower-spikes, the epistemonous petals varying at the same time from bright purple to pale pink or rarely white. But the white-flowered forms, sometimes mistaken in the past for D. grayi, have the characteristic calyx and bracts of D. pringlei. One very local form, recognized below as D. pringlei var. oxyphyllidia, combines in one plant a short-toothed calyx similar to that of D. grayi with purple petals. This variety, further distinguished from both typical D. pringlei and D. grayi by the relatively few pairs of large leaflets, has the wandlike growth-form of nearly sympatric D. pringlei var. multijuga. An extraordinary fund of variation in Thornbera is concentrated about the Conchos-Urique divide in western Chihuahua, and as exploration of this inaccessible and botanically little known region progresses, the problem of interspecific relationships in ser. Laevigatae may well need reappraisal.

It can now be seen that the type-collection of D. pringlei was from the edge of the species-range and is also morphologically marginal. The populations of D. pringlei in Arizona flower both in late summer (August-November) following summer rains and again, perhaps more reliably, in spring (February-May) as the temperatures rise and the days get longer. In most years the vernal form, to which the nomenclatural typus belongs, is a lowly, drought-inhibited plant, commonly with several stems up to ± 6 dm tall; the leaves developing with or soon before the flowers are relatively short and simple, with some 5 pairs of leaflets. The autumnal (exceptionally, in wet years, also vernal) phase develops somewhat taller stems that bear longer primary leaves composed of more numerous (up to 19, exceptionally 25) pairs of leaflets. It is not known that these two seasonal aspects occur in the same place, but I suppose this to be the case. In southern Sonora and Chihuahua, where D. pringlei is represented by the tall vars. oxyphyllidia and multijuga, no vernal phase is on record. Here the plants flower in autumn and winter, mostly from October into early March, by which time they are passing into summer dormancy and even though still bearing a few flowers have lost all but a few small upper leaves. The complicating factor of seasonal dimorphism in D. pringlei makes a concise, consistently useful key to its varieties almost unattainable.

References: [Article] Barneby, Rupert C. 1977. Daleae Imagines, an illustrated revision of Errazurizia Philippi, Psorothamnus Rydberg, Marine Liebmann, and Dalea Lucanus emen. Barneby, including all species of Leguminosae tribe Amorpheae Borissova ever referred to Dalea. Mem. New York Bot. Gard. 27: 1-892.

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