Description. Thallus as in U. angulata, but upper surface more often matte brown and less often with faint violet tones, to 12 cm diam, apothecia as in U. angulata but more quickly becoming rounded and elevated above the thallus; spores muriform, usually hyaline, sometimes pale brownish when overmature, 8 per ascus, 20–26(29) 3 13.5–15.5(17.5) mm.

Secondary chemistry. Not investigated.

Distribution. Southwest Oregon to southern California, including Sierra Nevada, Siskiyou, and San Bernadino Mountains.

Notes. Umbilicaria angulata and U. semitensis formed well-supported monophyletic groups, with one exception discussed below. These results support Tuckerman’s (1872) original distinction between these two species and contradict Llano’s (1950) conclusion that Umbilicaria semitensis should be treated as a synonym of U. angulata based on his hypothesis that the difference in spore septation and size reflect developmental stages. Although U. angulata and U. semitensis are indeed similar in external morphology and anatomy, apart from spore characters (see Llano 1950, Table 14, p. 177), the fact that we were able to separate them in the field on Mt. Bolivar in Oregon, suggests that subtle differences exist. These differences are, however, difficult to state unambiguously, such that they can be applied to other sites. Indeed Llano (1950) forcefully stated, ‘‘It is impossible to separate U. angulata Tuck. from U. semitensis Tuck. on gross morphological features.’’
While the word ‘‘impossible’’ is too strong, we recommend sectioning apothecia to check spores during routine identification. The apothecia of U.
semitensis are sometimes angular and somewhat depressed in the thallus but become sessile and roundish, while those of U. angulata are usually persistently depressed into the thallus and lenticular to angular or stellate; even when old and sessile they retain their irregular outline. At the Mt. Bolivar site, where the two species grow together, U. semitensis has a matte, light to dark brown upper surface, while U. angulata has a distinct semi-gloss
sheen and is darker brown, often with a faint violet tone.
Llano (1950) reported that the ‘‘distribution of these two species is the same,’’ yet he stated elsewhere that specimens with muriform spores were seen ‘‘only in collections from the vicinity of San Francisco Bay… and from Observatory Inlet, British Columbia (NY).’’ However, Tuckerman cites the Observatory Inlet specimen (herb. Hooker) as Umbilicaria angulata; and indeed we found simple spores in that specimen. Llano’s annotation on the
specimen from Observatory Inlet show that he too found simple spores, leaving us to conclude that he made an error in record keeping or memory in
reporting it to have muriform spores. This specimen, therefore, belongs to U. angulata s. str., leaving U. semitensis to be restricted to California and southern Oregon.
We found Umbilicaria angulata and U. semitensis to be largely allopatric, their ranges overlapping only in southern Oregon and northern California. So far we know of only one site where they co-occur: Mt. Bolivar, in SW Oregon. The southernmost site confirmed for U. angulata s. str. is in Plumas Co., California. Umbilicaria angulata appears to be rare in California. The type specimen, collected by Archibald Menzies, is labeled ‘‘Monterey.’’ Because we have confirmed no sites for U. angulata from central or southern California, and because Menzies traveled extensively along the north Pacific coast where U. angulata is common, we hypothesize that the type specimen is mislabeled as to locality. Menzies did collect near Monterey in the winter of 1792–93,
according to McKelvey (1956) and Eastwood (1924). It would be interesting to use Menzies’ journals to attempt to relocate his collecting sites near Monterey, then revisit in search of Umbilicaria. Apparently, Herre did just that, ‘‘…reported by Tuckerman as having been collected on maritime rocks at Monterey, but a careful search by me has failed to disclose it anywhere in the region’’ (Herre 1911). The most likely locations are Punta de Pinos and summit of the ridge west of the Presidio, based on descriptions of Menzies’ collecting in Eastwood (1924).
One specimen of Umbilicaria semitensis morph 2 is resolved, based on inferences from ITS or LSU data, as sister to the remaining three specimens of U. semitensis. Although we can not reject the hypothesis that this specimen is conspecific with U. semitensis, its sequences are roughly as divergent from those of the putative conspecific specimens, as are sequences of any two species. The data are insufficient to draw any taxonomic conclusions, but suggest a need for more sampling of U. semitensis, in particular the
morphological variant with short, broad, often flattened, black rhizines, usually accompanied by flat plates. The sole specimen of this was collected in
Yosemite National Park (McCune 30410). Other rhizinate Umbilicaria can occur with U. semitensis and U. angulata in western North America, most commonly U. polyrrhiza, which is easily separated by its ball-tipped rhizines that are coated with black thalloconidia (Hestmark 1990).
Umbilicaria torrefacta usually has a lower surface that is pale brown, with plates (trabeculae) and rhizines. Some specimens, however, have a blackish lower surface with relatively few trabeculae, giving the appearance of U. semitensis. Ambiguous cases are readily separated by observing the ascospores, which in U. torrefacta are less than half the size of U.
angulata. Umbilicaria phaea has apothecia that can be similarly angular and partly sunken in the thallus, but is usually easily distinguished from U. semitensis and U. angulata by lacking rhizines and trabeculae below. Occasional individuals of U. phaea can have a scattered rhizines, but these too can be separated definitively from U. angulata and U. semitensis by the relatively small spores of U. phaea. Other rhizinate species are easily separated by a grayer upper surface, including U. americana, U.
cinereorufescens, U. hirsuta, and U. vellea.