Adiantum shastense, a new species of maidenhair fern from California

Abstract A new species of Adiantum is described from California. This species is endemic to northern California and is currently known only from Shasta County. We describe its discovery after first being collected over a century ago and distinguish it from Adiantum jordanii and Adiantum capillus-veneris. It is evergreen and is sometimes, but not always, associated with limestone. The range of Adiantum shastense Huiet & A.R.Sm., sp. nov., is similar to several other Shasta County endemics that occur in the mesic forests of the Eastern Klamath Range, close to Shasta Lake, on limestone and metasedimentary substrates.


Introduction
Th e genus Adiantum L. (Pteridaceae) is found worldwide mostly in the tropics and subtropics, but about ten percent of species (of a total of ca. 225 spp.) are found in temperate regions. Th e majority of these occur in Asia but several are found in North America. Th ere are nine species of Adiantum in the continental United States and Canada and eight of the nine are native (Paris 1993). Th ree are of tropical origin, occurring in restricted ranges that are at their northern most limits. Th e remaining fi ve species occur solely in temperate regions, with four having a broad geographic range: Adiantum pedatum L., A. capillus-veneris L., A. aleuticum (Rupr.) C.A. Paris and A. jordanii Müll.Hal. Adiantum pedatum and A. capillus-veneris are distributed beyond North America (Paris 1993); A. capillus-veneris is the most wide-ranging and occurs on six continents, whereas A. pedatum occurs widely in both North America and Asia. Cytological data for diff erent geographic localities of these two species reveal diff ering chromosome numbers (diploids, tetraploids, dysploids), suggesting that they may both be species complexes (Löve and Löve 1997, Nakato and Kato 2005, Wagner 1963).
Of the four wide-ranging species, three Adiantum capillus-veneris, A. aleuticum and A. jordanii occur in California and none of these is endemic. Th ey all are found in at least 30% of the counties, and their distributions span the entire state. Adiantum aleuticum is easily recognized by its distinct pseudopedate laminar morphology, while A. jordanii has a laminar architecture that is more similar to A. capillus-veneris; however, the two are not closely related (Huiet et al. unpublished). Juvenile and sterile forms of these taxa can sometimes be diffi cult to distinguish.
While investigating Adiantum capillus-veneris populations in California as part of a worldwide molecular phylogenetic study of the genus, a new endemic species was discovered. Here we describe this new taxon and discuss its remarkable discovery after it was fi rst collected over 100 years ago.

Methods
Chromosome material of young sporangia was fi eld-fi xed in ethyl alcohol:acetic acid (3:1). Spore mother cells were stained with acetocarmine, and, using standard squash techniques, examined under a compound microscope. Meiotic cells were examined at diakinesis, metaphase I, and normal pairing of homologous chromatids was seen. Th e voucher is listed under paratypes.

Taxonomy
Adiantum shastense Huiet & A.R.Sm., sp. nov. urn:lsid:ipni.org:names:77148382-1 Figs 1-2 Diagnosis. Adiantum shastense is similar to A. jordanii in having dark brown to purplish brown rhizome scales and 2-3-pinnate laminae. It diff ers by being persistent and green throughout the summer, and does not die back as does A. jordanii. Adiantum shastense can be distinguished from A. capillus-veneris by the darker rhizome scales, the rhomboid shape of the pinnulets, and the often, glaucous bluish green color of the laminae.
Distribution and ecology. Adiantum shastense is currently known only from an area of the Eastern Klamath range (Miles and Goudy 1997) surrounding Shasta Lake entirely within Shasta County, California. It is found in mesic hardwood-conifer forests, on the forest fl oor as well as on limestone and metasedimentary rock outcrops, including rocky road cuts, most often in shade and with northern or eastern exposures. It co-occurs with the local endemic Shasta snow wreath, Neviusia cliftonii Shevock, Ertter & D.W.Taylor. In some localities it can be the dominant understory plant (Fig. 1a). Associated species include Pinus ponderosa P.Lawson & C.Lawson, Quercus chrysolepis Liebm., Acer macrophyllum Pursh, and Toxicodendron diversilobum (Torr. & A.Gray) Greene. Collected from 1100-2740 ft (335-835 m) elevation.
Phenology. Sporulates mid to late spring and most likely throughout summer. Etymology. It seems most appropriate to name this species Adiantum shastense, recognizing its restricted, currently known geographic localization to Shasta Co., California.
Suggested common name. Shasta maidenhair fern. Conservation status. We recommend a California Rare Plant Rank of 4.3, a watch list for plants of limited distribution.

Discussion
It was a surprise to discover that amongst the few herbarium collections of Adiantum from Shasta County, there was a previously unrecognized species. Before 2014, there were only 13 documented collections of Adiantum in the county (data from participants of the Consortium of California Herbaria, http://ucjeps.berkeley.edu/consortium). Amongst them were all the recognized taxa in California: A. aleuticum, A. capillusveneris, and A. jordanii. It was while confi rming the identity of a recent collection that we serendipitously stumbled upon the new species. DNA sequencing analysis revealed that this plant was neither A. capillus-veneris nor A. jordanii, but rather sister to A. jordanii. We confi rmed that additional specimens collected near Shasta Lake gave the identical result (Huiet et al. unpublished). Subsequently, in spring 2014, we made collections from additional populations across a wider geographic range to confi rm the earlier results and to examine material in the fi eld.
Morphologically Adiantum shastense has rhizome scales that are essentially the same as in typical A. jordanii. However the pinnulets of A. jordanii are more fan-shaped and usually the sorus length is much longer so there are fewer sori per pinnulet than in A. shastense. No doubt because of the shorter sorus length and the more cuneate shape to the pinnulets, A. shastense has been identifi ed by some as A. capillus-veneris, the only other species found in California with similar blade architecture. However, the sori of A. shastense have yellow farina among the sporangia, as does A. jordanii. Also, the rhi-zome scales of A. capillus-veneris are golden or lighter brown than those of A. shastense. Th e most striking diff erence between A. shastense and A. jordanii is that A. shastense is not ephemeral. Green laminae are persistent throughout the summer, and the fronds appear to overwinter without dying back, perhaps until more than a year's persistence. After the fronds die back, they ring the base of the plant, surrounding the new growth.
Th e fi rst collection of Adiantum shastense in Shasta County was over a century ago by Milo Baker and Frank Nutting, in 1894, and was identifi ed by Baker as A. jordanii. No other collection was made of A. shastense until 1992 (Taylor 12599, UC) and that was identifi ed as A. capillus-veneris. Subsequent collections were mostly identifi ed as A. capillus-veneris. Th us far, the distribution of A. shastense appears to be limited to a region surrounding Shasta Lake and the rivers and watersheds that feed into it and their drainages. A survey of other specimens identifi ed as A. jordanii and A. capillus-veneris from nearby areas (counties) did not reveal any additional collections of A. shastense. Th is includes a single collection of A. capillus-veneris from Siskiyou county (UC), collected in a cave at Lava Beds National Monument (Smith et al. 1993). We also have examined specimens of A. jordanii from Oregon and they too are correctly identifi ed.
It appears that the Shasta maidenhair fern is another narrow endemic found in the area surrounding Shasta Lake. Th is region is host to a number of endemic plants and animals, most likely because of its unique geology, age and climate. Th ese include the Shasta salamander, Hydromantes shastae Gorman & Camp, 1953(Hammerson et al. 2004; the Shasta monkey fl ower, Erythranthe taylori Nesom (Nesom 2013); Shasta snow wreath, Neviusia cliftonii (Lindstrand and Nelson 2006); and the Shasta eupatory, Ageratina shastensis (D.W.Taylor & Stebbins) R.M.King & H.Rob. (Taylor and Stebbins 1993). Of these species, the Shasta maidenhair fern has one of the widest geographic ranges, perhaps due to its wind-borne spores. Currently we do not know if its range extends beyond the geologically unique Shasta Lake region into neighboring counties. Further fi eld study may reveal more about this surprisingly new and unique California maidenhair fern. It currently is the only endemic species of Adiantum in the United States. California   1 Rhizomes stout, compact, short-creeping to suberect, usually 5-8 mm diam. (scales excluded); stipes mostly 1.5-3 mm diam. at bases; laminae palmatepinnate (fan-shaped), proximal pinna pair 2-3-times basiscopically forked; pinnulets strongly inequilateral, 2-4 times longer than wide .... A. aleuticum -Rhizomes relatively narrow, short-to long-creeping (occasionally more compact in A. shastense), usually 1.5-3 mm diam (scales excluded); stipes mostly 0.5-1.5 mm diam. at bases; laminae 2-3-pinnate (not fan-shaped), proximal pinna pair 0-1 times basiscopically forked; pinnulets more or less equilateral (bilaterally symmetric), about as long as wide or sometimes to twice as long as wide in A. capillus-veneris. Note: a combination of characters must occasionally be used to separate Adiantum capillus-veneris, A. jordanii, and A. shastense, i.e., not all characters are reliable for all specimens seen. However, the species characters for separating these three species are reliable for 95% or more of specimens seen. For example, Gross 2802 (UC), from Ventura Co., is undeniably A. capillus-veneris in rhizome characters, but blade characters resemble much more closely A. jordanii. Pinnulet characters (shape, distal margin) often vary, depending on size of fronds and extent of fertility. Rare, sterile hybrids showing intermediate morphology are known between A. aleuticum and A. jordanii (A. ×tracyi C.C.Hall ex W.H.Wagner), but no known hybrids are known between other species. In California, and probably elsewhere, the four species have rarely been found growing together. In Shasta Co., A. aleuticum and A. shastense have so far only once been found growing proximate to one another, but A. jordanii, does not co-occur with any of the other species, as far as we have observed.