Calasterella californica D. G. Long & T. X. Zheng. A 2023, comb. nov.

3. Calasterella californica (Hampe ex Austin) D.G.Long & T.X.Zheng, comb. nov.

Basionym: Fimbraria californica Hampe ex Austin, Hepat. bor.-amer. 33, 1873.

≡ Asterella californica (Hampe ex Austin) Underw., Bot. Gaz. 20: 60, 1895.

Representative specimens examined: MEXICO. Baja California: Cedros Island, 27 March 1952, G. Lindsay 17559 (HIRO). UNITED STATES. California: El Dorado County, American River at Folsom Lake, 290 m, 31 March 1998, D.G. Long 27540 (CAS, E00995790); Fresno Co., Sunnyside Road, west end of Pine Flat Lake, 310 m, 2 April 1998, D.G. Long 27552 (CAS, E00995793); Lake Co., Route 20 east of Clearlake Oaks, 660 m, 30 March 1998, D.G. Long 27533 (E00995789); Los Angeles Co., Angels Crest Highway above La Canada, 780 m, 7 April 1998, D.G. Long 27614 (E00995163); Marin Co., Cataract Creek, above Alpine Lake, 220 m, 16 March 2019, D.G. Long & J. Shevock 45892 (E01004900); Mariposa Co., Merced River Canyon at Slate Creek Bridge east of Briceburg, 390 m, 20 April 2017, D.G. Long & J. Shevock 44775 (E00997959); Napa Co., Wooden Valley Grade, 18 Mar. 1934, A. Carter 444 (NICH 201792); Nevada Co., north of Bridgeport on Pleasant Valley Road, 12 Apr. 1965, E. G. McLaughlin s.n. (NICH 262543); Riverside Co., Dripping Springs, Agua Tibia Wilderness, 460 m, 9 April 1998, D.G. Long 27651 (E00995160); San Benito Co., Pinnacles National Monument, between parking area and caves, 350 m, 27 April 2006, W. T. Doyle 11445-b (E01004302). Western foothills of the Gabian Range, San Juan Grade Road, County Road 3, just west of the 1.21 mileage marker, 154 m, 19 March 2010, W. T. Doyle 11553 (CAS, TNS); San Bernardino Co., San Gabriel Mountains, near Lytle Creek, 740 m, 8 April 1998, D.G. Long 27624 (E00995162); San Luis Obispo Co., Los Padres National Forest West Cuesta Ridge on TV Tower Road, 640 m, 30 March 2019, D.G. Long & J. Shevock 45940 (E); Santa Clara Co., Los Altos Hills, 31 Aug. 1971, W. B. Schofield s.n. (NICH 306406), do., 10 Mar. 1993, W. B. Schofield 98595 (NICH 428742); Sonoma Co., route 128 NW of Cloverdale, 200 m, 27 March 1998, D.G. Long 27481 (E00995788); Tulare Co., east side of Lake Kaweah near Three Rivers, 219 m, 7 March 2017, D.G. Long, J. Shevock & W.-Z. Ma 44666 (E00997960); Tuolumne Co., Columbia, 1.0 mile above Parrott’s Ferry Bridge over the Stanislaus River, 2 July 1966, D. M. J. Mueller 6703 (NICH 298550); Ventura Co., Creek Road, Ojai, 23 Mar. 1927, N. B. Kimber 2894 (NICH 216581). Oregon: Josephine Co., south side of Rogue River along trail to Raine Falls below Grave Creek Bridge, 205 m, 25 March 2018, D.G. Long & J. Shevock 45333 (E00997086).

Taxonomic notes: Based on the morphological and phylogenetic evidence, we here establish Calasterella D.G.Long & T.X.Zheng as the seventh genus of the family Aytoniaceae. This genus may be confused with Mannia and Reboulia given that they share a similar appearance and female receptacle, respectively (Bischler 1998; Bischler-Causse et al. 2005). However, both Mannia and Reboulia show absence of a pseudoperianth (except Mannia gracilis (Weber 1815: 105) Schill & Long (2010: 173)) but display dichotomous, ventral or terminal innovative thallus branching while Calasterella has dichotomous branching only. In addition, Mannia possesses (1) aromatic plants, (2) depressed hemispherical or subglobose female receptacles, and (3) cup-shaped involucres (Schill 2006). Reboulia has (1) bilabiate involucres, (2) ventral scales with 2–3(4) filiform appendages, (3) 4–7-lobed receptacles and (4) yellowish brown coarsely areolate spores (Bischler 1998; Bischler-Causse 2005). Calasterella can be confused with Asterellopsis because both taxa have dichotomously branching thalli. The latter, however, is distinguished by (1) fewer (1–2) and sometimes unequally bifid ventral scale appendages, (2) spherical female receptacles, and (3) dark brown or black spores with germinal apertures. When sterile, Calasterella is more or less similar to Preissia Corda (1829: 647) and Bucegia Radian (1903: 3) (Marchantiaceae). However, the latter two genera can be readily differentiated by their compound air pores (Zheng & Shimamura 2022). The only other dioicous species traditionally placed in Asterella is the Asiatic A. wallichiana (Lehmann & Lindenberg 1832: 4) Grolle (1966: 262), but as pointed out by Long (2006) the latter is readily distinguished by the complete cessation of vegetative growth at the apex of the thallus of female plants, whereas in C. californica vegetative growth continues from the lateral lobes at the thallus apex (Haupt 1929: Fig. 9).

Traditionally, Aytoniaceae was divided into two subfamilies (Grolle 1983; Grolle & Long 2000), Aytonioideae (Plagiochasma) and Reboulioideae (Asterella s. lat., Cryptomitrium, Mannia, and Reboulia). However, recent phylogenetic studies on complex thalloid liverworts have proposed a different conclusion (Villarreal et al. 2016; Xiang et al. 2022), in which Aytoniaceae is resolved into five major clades, namely Asterella s. str., Asterellopsis - Cryptomitrium, Calasterella, Mannia and Reboulia - Plagiochasma, and this grouping is inconsistent with the traditional bipartite classification of the family. Previously, the presence of pseudoperianths was regarded as a unique character that distinguished Asterella s. lat. from other genera of the family (Long 2006). However, the recent studies by Schill et al. (2010) transferred A. gracilis to Mannia, and Xiang et al. (2022) established a new genus Asterellopsis based on the species Asterella grollei Long (1999: 102), indicating that the pseudoperianth is probably a plesiomorphic feature, and the morphology of spores might be used as a more informative character to underpin the classification within Aytoniaceae (Long 1998; Schill 2006; Schill et al. 2010). To solve this problem and propose an amended classification of Aytoniaceae at subfamily level, phylogenetic studies involving more samples from a wide geographical range are now nearing completion.