Description of a new species of the genus Mallomonas from section Mallomonas (Synurales, Chrysophyceae) in the tropics Author Gusev, Evgeniy 0000-0002-7397-5808 evsergus @ yahoo. com; https: // orcid. org / 0000 - 0002 - 7397 - 5808 evsergus@yahoo.com Author Shkurina, Nikita Martynenko Nataliya Author Dien, Tran Duc 0000-0002-9512-1336 Coastal Branch of Joint Vietnam-Russia Tropical Science and Technology Research Center, 30 Nguyen Thien Thuat, Nha Trang 650000, Vietnam & mrtran _ cnvb @ yahoo. com; https: // orcid. org / 0000 - 0002 - 9512 - 1336 mrtran_cnvb@yahoo.com text Phytotaxa 2023 2023-09-29 618 1 59 68 http://dx.doi.org/10.1094/PDIS-04-22-0755-PDN journal article 10.11646/phytotaxa.618.1.5 1179-3163 8389917 Mallomonas pseudocorymbosa Gusev, Martynenko & Shkurina sp. nov. ( Figure 2 ). Diagnosis: Scales are oval, tripartite, 4.8–5.9 × 3.3–4.3 µm in size, with or without a dome. The dome is large, rounded, oval or asymmetrical. The V-rib is acute, slightly hooded and its arms continuous with the anterior submarginal ribs. Anterior submarginal ribs are well developed. The anterior flange is wide, especially on the domeless scales, with a row of base plate pores at each side. The posterior flange is wide, with numerous base plate pores distributed on the surface. The shield and posterior flange have a secondary siliceous layer forming circular or elongated oval meshes unevenly distributed on the surface often with areas without development of the secondary layer. Numerous pores are placed on the basal plate. The posterior upturned rim is narrow, with inner struts visible only on TEM images, encircles less than a half of the scale perimeter. Bristles are 13–25 μm long, curved and serrated at the distal half. Shorter bristles have a bifurcated tip with a long terminal spine, and longer bristles have a prolonged thread-like terminal part. Cysts unknown. Holotype (here designated): Portion of a single gathering of cells on SEM stub No. CD 8 deposited at the Herbarium , Papanin Institute for Biology of Inland Waters RAS , Borok ( IBIW ). Material from Ahn Hai Lake , Côn SƠn Island, Bà R ịa-Vũng Tàu Province , Vietnam . Figure 2C illustrates a representative scale from the holotype specimen. Type Locality: Ahn Hai Lake , Côn SƠn Island, Bà R ịa-Vũng Tàu Province , Vietnam . Latitude / Longitude : 8° 40.645’ N 106° 35.867’ E . At the time of collection, the pH was 6.5, temperature 30 °C, and specific conductance 201 µS cm-1 . Material was collected by E.S. Gusev and Nguyen-Ngoc Lam on 3 May 2015 . Etymology: The species name is derived from the fact that its scales resemble, and could be confused with, those of Mallomonas corymbosa . Distribution: This species has been observed in 17 localities in 13 provinces of Vietnam ( Table 1 ). Scales of this species were also observed in Bangladesh ( Takahashi & Hayakawa 1979 ), China ( Wei &Yuan 2001 , 2013; Wei et al . 2014 ), Brazil ( Franceschini & Couté 1991 )and South Africa ( Janse van Vuuren et al . 2022 ). Mallomonas pseudocorymbosa was found at wide ranges of environmental parameters: pH from 6.1 to 8.6, specific conductance from 62 to 2370 µS cm-1 , chlorophyll a values from 5 to 76 µg l –1 , and temperature 17–39 ºC ( Table 1 ).