Quaeritorhiza haematococci Longcore, D.R. Simmons, T. Y. James & S. Qin, sp. nov.  FIG. 1A–K

MycoBank number: MB 833715; Index Fungorum number: IF 833715; Facesoffungi number: FoF;

Typification: USA. TEXAS: Northeast Texas, host Haematococcus pluvialis, Jun 2017, S. Qin (holotype FIG. 1A–K). Ex-type culture JEL0916 (CZEUM– MICH). GenBank: 28S = MN587036; 18S = MN586917.

Description: Thallus monocentric, with one rhizoidal axis often swollen at the base; primary rhizoids clustered and repeatedly branched at the tip of the major axis, later-developing rhizoids extend farther into the medium and less frequently branched; becoming inter- biotic on host. Generation time on PmT nutrient agar 3–7 d at 30 C. Zoospores release through 1–4 inoperculate discharge pores or broad tubes. Zoospores briefly elongate upon emergence, spherical when in motion, ~5–6 µm diam; flagellum ~ 25 µm in length. Grows well in groups on nutrient agar, but scattered zoospores rarely survive. Resting spores form in inoculated host culture. Parasitic on Haematococcus pluvialis.

Etymology: haematococci (Greek), in reference to the genus of the host.

Figure 1. Morphology of Quaeritorhiza haematococci life cycle (isolate JEL0916) on PmT agar (A–I) or on Haematococcus cells (J, K) incubated at 30 C for 12 d. A. Spherical zoospores. B, C. One-day-old germlings with major rhizoidal axes terminated with a clump of branched rhizoids. D. One-day-old germling with rhizoidal axis terminated by branched rhizoids plus unbranched, “seeking” rhizoids (arrows) arising near the rhizoidal base. E. Three-day-old thallus with apophysis (arrowhead). Arrow indicates seeking rhizoid. F. Zoosporangium with branched rhizoids plus less-branched, seeking rhizoid (arrow) extending beyond clumped rhizoids. Arrowhead indicates apophysis. G. Nearly mature zoosporangium with two discharge papillae; arrowhead indicates apophysis. H. Stacked images of nearly mature zoosporangium with three discharge papillae (arrows). I. Zoospores discharging from small zoosporangium with single, short discharge papilla (arrow). J. Large resting spore (26 µm diam) with single lipid globule and thick, crenulated wall. K. Smaller (12 µm diam) resting spores surrounded by dead host thalli. Bar in B = 10 µm for all parts of the figure.