Monardella Stebbinsii ( Lamiaceae ) , A New Serpentine Endemic Species from the Northern Sierra Nevada , Plumas County , California

M onarde/la stebbinsii (Lamiaceae ), a new species from the northern Sierra Nevada of Plumas County, California, is described and illustrated. Characterized by ovate leaves, multiple verticillasters per infiorascence, a matlike habit, reddish papery bracts, and purplish-red leaves with a soft white pubescence, the species is not closely related to any other species of the genus. The new species is apparently restricted to the central portion of a serpentine outcrop located north and east of the confluence of the North Fork of the Feather River and its East Branch.


MORPHOLOGY AND AFFINITIES
The inflorescence in Monardella, as in Monarda (Scora 1966), is a verticillaster; a false whorl composed of a condensed pair of essentially sessile, determinate cymes (dichasia).Unlike Monarda, the inflorescence is subtended by two pairs ofleaflike bracts, which make up the outer set ofbracts (Hardham 1966b).Though the first pair of bracts also may be petiolate, and attached a centimeter or two below the verticillaster, the outer set of bracts or "leafy bracts" in M. stebbinsii typically are purplish-red and membranous (except for the leafy green tip), and closely subtend the verticillaster.However, the leafy bracts are highly variable and can be green and leaflike in M. stebbinsii, as in some other species with colored bracts (e.g., M. linoides Gray and M. glauca Greene).Three pairs of highly modified membranous bracts (one pair of "cyme bracts" per inflorescence and one pair of "cymule bracts" for each dichasium and supporting stem) compose the middle set of bracts.These bracts are wide-ovate, reddish, and papery in M. stebbinsii.In M. stebbinsii, like other species with colored bracts, the cyme bracts are merely smaller versions of the second pair ofleafy bracts.A pair of"bracteoles" immediately subtend each dichasium and form the inner set of bracts in the inflorescence.Even when present, these acicular, translucent-membranous bracts are difficult to see.Moreover, the bracteoles are often essentially absent, especially when the leafy bracts are somewhat papery and red.As a result, the bracts of M. stebbinsii appear to be intermediate between the presumed primitive (leafy bracts green and leaflike) and derived condition (leafy bracts somewhat papery and colored, and the middle and inner set of bracts much reduced to absent).
The entire, ovate, and relatively small, thick leaves of M. stebbinsii often have a curious ashy to lead-gray to plum color due to a combination of soft white pubescence and purplish-red pigments that masks the green.Both leaf surfaces may be reddish, especially the adaxial surface near the apex.
The affinities of M. stebbinsii may lie with other narrowly endemic species (e.g., M. cinerea Abrams, M. australis Abrams).These endemics have reddish papery bracts and are often diploid and pubescent.Regardless, the presence of ovate leaves and multiple verticillasters per inflorescence combined with the matlike habit (Fig. 2), reddish papery bracts, ploidy, and leaf vestiture and coloration of the species clearly indicate that M. stebbinsii is not closely related to any known species.Monardella stebbinsii would be placed in sect.Odoratissimae in Epling's ( 1925) treatment of the genus, a section that is largely distributed in the Sierra Nevada, Cascade Mountains, and mountain ranges of the Great Basin.The value of assigning the species to an existing section is of dubious value, however, given the lack of any close allies to M. stebbinsii.
Chromosome counts varied between plants.Aneuploid chromosome numbers seem to be common in many species of Monardella (Hardham 1966a(Hardham , 1966b, ,  unpubl.data).El-Gazzar and Watson (1970) suggested that the base number of .X = 7 for that group of Lamiales in which they included Monardella.However, as a result of numerous counts by the first author and work by Raven et al. (1965), the base number for the genus appears to be 21.

DISTRIBUTION, ECOLOGY, AND PHENOLOGY
Monardella stebbinsii apparently is narrowly restricted to the central portion of a northwest-southeast trending, ultramafic geologic body consisting largely of serpentinite ("serpentine").This area of serpentine, which is north and east of the confluence of the North Fork of the Feather River and its East Branch (Fig. 3), is the northernmost ultramafic body in the Sierra Nevada (Kruckeberg 1984).The species occurs mostly as widely scattered individuals on steep, loose slopes of generally reddish serpentine talus and boulders, between 820 and 1900 m.
The talus slopes harboring M. stebbinsii support only a sparse vegetation, unlike the serpentine sites occupied by chaparral or mixed evergreen forest.Although serpentine generally reduces and attenuates the vegetation ("serpentine syndrome") (Jenny 1980), the sparsely vegetated to barren serpentine found at the type locality and largely at the other population localities reflects the severity of this habitat (Kruckeberg 1984).Nonetheless, the new species obviously tolerates these extreme conditions (i.e., semistable loose talus slopes, skeletal serpentine soils with little available moisture), which effect the sparse vegetation.Although we cannot explain the absence of M. stebbinsii from adjacent, more-vegetated, serpentine habitats, tolerance to a narrowly defined habitat enable M. stebbinsii to occupy sites essentially devoid of competitors.
Monardella stebbinsii typically flowers from July to early September.At higher elevations (1900 m), individual plants likely flower, to some degree, throughout September.This flowering period, which is largely later than that of other monardellas growing on and off serpentine in the area, is remarkable given the hot and dry conditions prevalent at that time.The few competing plants and the pubescence of the species are two factors that may contribute to the apparent drought tolerance of M. stebbinsii.
As with other monardellas (Hardham 1966a(Hardham , 1966b;;Shevock et al. 1989), an examination of some individuals of M. stebbinsii and two sympatric taxa (M.rejlexa, M. odoratissima var.follettii) suggests that some introgression has occurred in the general area.For example, M. reflexa, which typically is glabrous in the general area, produces marginally pubescent and somewhat purplish leaves near the type locality of M. stebbinsii.Populations of M. odoratissima var.follettii growing on Red Hill and to the west near Yellow Creek often have dark purple leaves on the upper portion of the stem.Compared to the M. stebbinsii growing elsewhere, the plants occurring south of Serpentine Canyon have more elliptical, slightly less pubescent leaves that lack any plum coloration.However, similar individuals can be found within the central portion of the large population at the type locality, which is devoid of sympatric species.Despite the apparent hybridization occurring between M. stebbinsii and these other monardellas, we do not believe these minor morphological variations weaken the distinctiveness of M. stebbinsii due to the several morphological characters unique to the new species.