Prodr. 10: 454. 1846
Herbs, perennial; rhizomatous. Stems erect when aerial, horizontal to erect when subterranean, glabrous. Leaves basal, helical; petiole present; blade not fleshy, leathery or not, margins with simple or compound teeth and some lobes deeply incised to pinnatifid. Inflorescences axillary, racemes, erect or decumbent; bracts present. Pedicels present; bracteoles absent. Flowers bisexual; sepals 2–4(or 5), basally connate, calyx bilaterally symmetric, campanulate, lobes ovate to lanceolate; corolla white, yellow, green, pink, reddish, lavender, or blue to bluish purple, bilaterally symmetric, bilabiate or ± regular (unilabiate in S. rubra), campanulate, tubular, ellipsoid, or rudimentary, tube base not spurred or gibbous, lobes 0 or 3 or 4(or 5), abaxial 2 or 3(or 4), adaxial 1; stamens 2, epipetalous or inserted on receptacle, filaments glabrous; staminode 0; ovary 1-locular, placentation parietal centrally, axile distally and proximally; stigma capitate. Fruits capsules, flattened, dehiscence loculicidal and basipetal over apex. Seeds 2–40, brown, disc- or boat-shaped (S. cordata, S. reniformis), wings absent. × = 12.
North America, n Mexico.
Species 19 (19 in the flora).
Plants of Synthyris flower in the early spring and as early as snowmelt in alpine and tundra areas, and fruits mature by mid spring. Flowers are protogynous. Species of Synthyris are not consistent with Darwin's pollination syndrome that associates acropetal floral maturation with protandry and upward movement of pollinators on the inflorescence; instead, insect visitors (primarily pollen foraging bees) show a weak tendency to move vertically among the protogynous flowers with both self- and cross-pollination (M. J. McCone et al. 1995).
Synthyris occurs in arctic and alpine tundra, grasslands, savannas, and mesophytic forests. Some species have restricted distributions, and two are of conservation concern.
Synthyris is part of a monophyletic Veroniceae that includes Veronica and allied genera. The closest relatives of Synthyris are uncertain and may be either clades of Veronica or Asian Veroniceae (Albach et al. 2004; D. C. Albach and H. M. Meudt 2010).
Species treated as Besseya by P. A. Rydberg (1903), F. W. Pennell (1933), and C. G. Schaack (1983) are monophyletic in Synthyris. The bilabiate flowers and more coriaceous leaves characteristic of the besseyas are derived in Synthyris. Dissected leaves are convergent in Synthyris, evolving independently in S. pinnatifida and the clade consisting of S. canbyi, S. dissecta, and S. lanuginosa, in association with shifts into alpine and treeline environments (L. Hufford and M. McMahon 2004). Synthyris cordata and S. reniformis are low elevation species of moist forests that uniquely share decumbent infructescences, an apparent specialization for seed dispersal by ants.
|1||Leaves strictly annual, disintegrating in 1st year; leaf blade margins crenate or incised-crenate; corollas bilabiate, unilabiate (S. rubra), or absent (S. wyomingensis), longer than or as long as calyces, or corollas rudimentary or absent.||> 2|
|2||Petals 0 or 1–4, rudimentary if present, corollas much shorter than calyces if present.||> 3|
|3||Sepals 4, basal connation between abaxial and adaxial lobes on each side of flower; petals 1–4, rudimentary.||Synthyris rubra|
|3||Sepals 2–4, all lobes connate, if 2+ lobes then connate for at least 1/2 of length on abaxial side; petals 0.||Synthyris wyomingensis|
|2||Petals 3 or 4(or 5), corollas nearly as long as or longer than calyces.||> 4|
|4||Corollas blue, bluish purple, lavender, or reddish.||Synthyris alpina|
|4||Corollas white, yellow, or pink.||> 5|
|5||Corollas yellow.||> 6|
|6||Basal veins of leaves extending into distal 1/2 of blade, lateral veins 3–6 on each side of midvein; corolla tubes conspicuous; stamens epipetalous; ovaries puberulent to villous.||Synthyris bullii|
|6||Basal veins of leaves extending through basal 1/2 of blade, lateral veins 5–12 on each side of midvein; corolla tubes absent; stamens inserted on receptacles, abaxial and adaxial petal lips basally adnate to stamens; ovaries glabrous or sparsely hairy at apex.||Synthyris ritteriana|
|5||Corollas pink to white.||> 7|
|7||Corollas 2–3 mm longer than calyces; ovaries puberulent to villous at apex; Sierra Blanca Range, New Mexico.||Synthyris oblongifolia|
|7||Corollas 0–2 mm longer than calyces; ovaries glabrous; Arizona, Colorado, New Mexico, Wyoming.||Synthyris plantaginea|
|1||Leaves persistent, some withering in 2d year as new leaves expand; leaf blade margins dentate, crenate, incised-crenate, laciniate, pinnately lobed, or ± palmately lobed; corollas ± regular, much longer than calyces.||> 8|
|8||Racemes decumbent, sterile bracts usually 0.||> 9|
|9||Leaf blades ovate to ovate-cordate; corollas glabrous.||Synthyris cordata|
|9||Leaf blades cordate to reniform; corollas puberulent-villous in throat.||Synthyris reniformis|
|8||Racemes erect, sterile bracts 2 or 3+.||> 10|
|10||Petal apices laciniate.||> 11|
|11||Racemes ovate-spatulate, largest sterile bracts less than 1 cm; Idaho.||Synthyris platycarpa|
|11||Racemes fan-shaped, largest sterile bracts 2+ cm; nw Oregon, w Washington.||Synthyris schizantha|
|10||Petal apices entire or erose.||> 12|
|12||Leaf blade margins laciniate, ±incised-crenate, dentate, or ± palmately lobed.||> 13|
|13||Capsules hairy; Northwest Territories, Yukon, Alaska.||Synthyris borealis|
|13||Capsules glabrous, glabrescent, or sparsely hairy; nw United States.||> 14|
|14||Leaf blades less than 25 mm wide; corolla tubes inconspicuous.||Synthyris ranunculina|
|14||Leaf blades 25+ mm wide; corolla tubes conspicuous.||> 15|
|15||Leaf blades ovate or cordate, margins ± incised-crenate or laciniate to ± pinnatifid, sometimes ± palmately lobed; Montana.||Synthyris canbyi|
|15||Leaf blades orbiculate, reniform, or cordate, margins ± laciniate or ± incised-crenate to dentate, sometimes palmately lobed; California, Idaho, Montana, Oregon, Utah, Washington.||> 16|
|16||Leaf blade margins ± laciniate, sometimes palmately lobed or incised-crenate; Utah.||Synthyris laciniata|
|16||Leaf blade margins ± incised-crenate to dentate; California, Idaho, Montana, Oregon, Washington.||Synthyris missurica|
|12||Leaf blade margins pinnately lobed or 1–3-pinnatifid.||> 17|
|17||Leaf blade surfaces canescent or tomentose.||> 18|
|18||Leaf blade surfaces tomentose; adaxial petals flat; ec Idaho, sw Montana.||Synthyris dissecta|
|18||Leaf blade surfaces canescent; adaxial petals not flat; nw Washington.||Synthyris lanuginosa|
|17||Leaf blade surfaces glabrous, sparsely hairy, puberulous, or villous.||> 19|
|19||Capsules hairy.||> 20|
|20||Ovaries sparsely hairy at apices; flowers 10–50; Montana.||Synthyris canbyi|
|20||Ovaries pilose to tomentose; flowers 10–30; ec Idaho, Montana.||Synthyris dissecta|
|19||Capsules glabrous.||> 21|
|21||Leaf blade margins ± pinnatifid, teeth apices obtuse to rounded, surfaces sparsely hairy; Montana.||Synthyris canbyi|
|21||Leaf blade margins 1- or 2-pinnatifd, teeth apices obtuse to acute, surfaces glabrous or villous; Idaho, Utah, Wyoming.||Synthyris pinnatifida|