Prodromus of a fern flora of Bolivia. XLII. Update I. Author Kessler, Michael Systematic and Evolutionary Botany, University of Zurich, Zollikerstrasse 107, CH- 8008 Zurich, Switzerland. Author Smith, Alan R. University Herbarium, 1001 Valley Life Sciences Bldg. # 2465, University of California, Berkeley, CA 94720 - 2465. Author Øllgaard, Benjamin Department of Biology - Ecoinformatics and Biodiversity, Ny Munkegade 116, building 1137, 8000 Aarhus C, Denmark. Author Matos, Fernando B. Centro de Referência em Informação Ambiental (CRIA), Rua João Carlos do Amaral 500, 13070 - 111, Campinas, SP, Brasil. Author Moran, Robbin C. New York Botanical Garden, 2900 Southern Blvd., Bronx, New York, 10458 - 5126, USA. text Phytotaxa 2023 2023-12-20 630 3 183 210 https://phytotaxa.mapress.com/pt/article/download/phytotaxa.630.3.2/51376 journal article 10.11646/phytotaxa.630.3.2 1179-3163 10409920 Serpocaulon rex Schwartsb. & A.R.Sm., J.Bot. Res. Inst. Texas 7(1): 86–88, f. 1. 2013. Range:— Ecuador to Bolivia (PA, SC), Brazil , and Paraguay ( Sanín et al. 2023 ). Schwartsburd & Smith (2013) described this species as a narrow endemic to the Atlantic rain forest and seasonal semideciduous forest from Brazil . Sanín et al. (2019 a , 2023) extended this distribution to Goias and Mato Grosso do Sul states, as predicted ( Schwartsburd & Smith 2013 ). Here, its range is now known still wider in Brazil , as well as in neighboring countries. Ecology:— Rare, epiphytic in lowland swampy ecosystems, along the margins of streams of seasonal forests, at 0‒ 700 m . Notes:— Serpocaulon rex most resembles S. attenuatum and S. triseriale , which also have thick rhizomes ( 6‒20 mm ) with abundant pubescent roots, lanceolate rhizomes scales with patent apex, and impressed veins. However, S. rex differs from S. attenuatum by the long-creeping rhizome (vs. short-creeping), pinnate blades (vs. proximally pinnate and distally pinnatisect), and more rows of sori between the costae and pinna margins (3–6(–7) vs. 1(–2) rows). From S. triseriale , S. rex differs by the long-creeping, subterranean rhizome (vs. short-creeping and exposed), rhizome scales with clear lumen in the center of each cell (vs. colored lumen in cell-centers), pinna margins cartilaginous and crenate (vs. not cartilaginous and entire), and more rows of sori between the costae and pinna margins (3–7 vs. 1–4 rows). Sanín et al . (2023) listed the following specimens for Bolivia : Pando : Manuripi , ca. 20 km S of Río Manuripi on the road to Chivé , 11°58’ S , 68°35’ W , 12 Aug 1982 , Sperling & King 6595 ( BRIT *, F , MO , NY *, TEX , US *, WIS *) ; Santa Cruz : Nuflo de Chavez , 5 km al N de Perseverancia , 257 m , 14°38’ S , 62°37” W , 11 June 1990 , Vargas 586 ( F *) . ( Serpocaulon silvulae (M.Kessler & A.R.Sm.) A.R.Sm. , Taxon 55(4): 929. 2006 .) According to Sanín et al . (2023) , this species is not distinct from S. crystalloneuron .