Key 1:

SECTION 1:
Sporangium predominantly spherical or sub-spherical throughout development.

Section 1

1. Principally from a terrestrial (soil) habitat............................................2
Principally from an aquatic (freshwater or marine)habitat..........................23

2. Zoospores discharged in a vesicle.......................................................3
Zoospores discharged singly, consecutively, but not in a vesicle..................6

3. Discharge apparatus one or more papillae............................................4
Discharge apparatus a pore with a recurved rim, sporangial wall double - contoured............................................................................R. lenelangei

4. Discharge apparatus 1-5 papillae, sporangium with conspicuous concentric halos......................................................................................R. coronum
Discharge apparatus 1 apical or lateral papilla, sporangium without halos.....5

5. Rhizoids sparse, branched, thalli numerous (up to 14) on host cell.............. ...........................................................................................R. amoebae
Rhizoid unbranched, an intramatrical peg or foot....................R. aphanomycis

6. Discharge apparatus one or more papillae or pores ................................7
No papillae or pores present; zoospores released when sporangial wall dissolves or collapses ...................................R. patellarium (=R. collapsum)

7. Discharge apparatus one or more papillae..............................................8
Discharge apparatus one or more pores....................................................19

8. Discharge apparatus a single papilla......................................................9
Discharge apparatus multiple papillae......................................................10

9. Discharge apparatus one apical or lateral papilla, zoospores released singly ..............................................................................R. ellipsoideum
Discharge apparatus one apical papilla, zoospores released simultaneously... ...............................................................................................R. aureum

10. Organism parasitic on Nowakowskiella...........................R. rarotoganensis
Organism saprophytic on pollen, chitin, or keratin......................................11

11. Organism saprophytic on chitin or keratin...........................................12
Organism saprophytic on pollen..............................................................16

12. Organism saprophytic on chitin............................................R. signyense
Organism saprophytic on keratin.............................................................13

13. Sporangium stalked..........................................................R. stipitatum
Sporangium sessile...............................................................................14

14. Discharge apparatus 5-10 papillae, sporangial wall ornamented............... .....................................................................................R. keratinophilum
Discharge apparatus 2-30 papillae, sporangial wall ornamented...................15

15. Discharge apparatus 1-30 (av. 16) papillae, zoospores 2-3micrometers diam., discharged simultaneously from several papillae.............R. condylosum
Discharge apparatus 5-10 papillae, zoospores 5-7micrometers diam., discharged from one or two papillae..........................................R. piligenum

16. From halophytic soils.......................................................R. halophilum
Not from halophytic soils......................................................................17

17. Discharge apparatus 2-5 papillae, sporangial wall distinctly double-contoured........................................................................R. sphaerotheca
Discharge apparatus 3-many papillae, sporangial wall not double-contoured ...........................................................................................18

18. Discharge apparatus 3-12 papillae, rhizoids hair-like..........R. capillaceum
Discharge apparatus multiple papillae, rhizoids originate as multiple robust, closely spaced axes on base of sporangium............................R. brooksianum

19. Discharge apparatus a single pore.................................R. marshallense
Discharge apparatus multiple pores........................................................20

20. Sporangial wall ornamented with 3-50 elongate, flexible, unbranched hairs...............................................................................R. hispidulosum
Sporangial wall not ornamented..............................................................21

21. Thalli numerous (up to 80) on host, primarily parasitic on Rhizophlyctis rosea and other chytrids ...............................................R. hyperparasiticum
Thalli single or few on host...................................................................22

22. Organism saprophytic on cellulosic substrata......................R. polystomum
Organism saprophytic on pollen.................................................R. bullatum

23. From marine habitat.......................................................................24
From freshwater habitat.......................................................................28

24. Discharge apparatus 1 or more papillae.............................................25
Discharge apparatus 1-several pores, or a large, lateral, irregular aperture..27

25. Discharge apparatus a single apical or lateral papilla............................. ............................................................................R. brevipes v. marinum
Discharge apparatus 2-16 papillae..........................................................26

26. Discharge apparatus 2-3 low papillae, sporangium 13-26 micrometers diameter................................................................................R. littoreum
Discharge apparatus 5-16 papillae, sporangium 24-41 micrometers diameter .............................................................................R. aestuarii

27. Discharge apparatus 1-several pores, sporangium 30-60 micrometers diameter..........................................................................R. subglobosum
Discharge apparatus a large, lateral, irregular aperture, sporangium 16-24 micrometers diameter...............................................................R. codicola

28. Rhizoids extramatrical........................................................R. sparrowii
Rhizoids intramatrical...........................................................................29

29. Zoospores discharged in a vesicle.....................................................30
Zoospores discharged singly, consecutively, or as a group, but not in a vesicle ...............................................................................................33

30. Discharge apparatus 1-5 low papillae.............................R. macrosporum
Discharge apparatus a single apical pore, or sporangial apex deliquesces.... .........................................................................................................31

31. Sporangial apex deliquesces.........................................R. planktonicum
Discharge apparatus a single apical pore................................................32

32. Sporangial wall persists after discharge...............................R. rotundum
Epibiotic portion of sporangium deliquesces after....................................... discharge..........................................................................R. poculiforme

33. Discharge apparatus a tube, or 1 or more pores papillae, or beaks.......34
No discharge apparatus; sporangial wall deliquesces to release zoospores .........................................................................................69

34. Discharge apparatus 1-2 sub-apical beaks.........................R. rostellatum
Discharge apparatus a tube, or 1 or more pores or papillae.......................35

35. Discharge apparatus a tube............................................................36
Discharge apparatus 1 or more pores or papillae.....................................37

36. Sporangium 6-8 micrometers diameter, discharge tube 4-5 micrometers long by 2 micrometers diameter.........................................R. ampullaceum
Sporangium 32-58 micrometers diameter, discharge tube 6 micrometers long by 4.5 micrometers diameter.................................................R. deformans

37. Discharge apparatus 1 or more papillae............................................38
Discharge apparatus 1 or more pores.....................................................51

38. Discharge apparatus a single papilla................................................39
Discharge apparatus 1-5 (usually multiple) papillae.................................43

39. Discharge papilla apical, prominent, slightly oblique......R. asymmetricum
Discharge papilla apical or subapical, not oblique...................................40

40. Sporangium small, up to 7 micrometers diameter, rhizoidal system delicate, unbranched or once-branched .....................................R. schroeteri
Sporangium larger, 10-33 micrometers diamete......................................41

41. Sporangium 10-13 micrometers diameter, endobiotic part a lobate, sac-like haustorium................................................................................R. skujai
Sporangium 10-33 micrometers diameter, endobiotic part a branched............ rhizoid..............................................................................................42

42. Sporangium 10-33 micrometers diameter, discharge papilla................... apical............................................................................R. mammillatum
Sporangium 10-20 micrometers diameter, discharge papilla......................... lateral................................................................................R. punctatum

43. Sporangia proliferate internally.........................................R. proliferum
No internal proliferation of sporangia.....................................................44

44. Thalli numerous (up to 20) on host.................................R. chytriomycii
Thalli few on host...............................................................................45

45. Organism saprophytic on pollen.......................................................46
Organism parasitic..............................................................................47

46. Sporangium 8-15 micrometers diameter, with usually 2 or more subapical papillae ............................................................................R. squamosum
Sporangium 22-35 micrometers diameter, with 1-5 variously placed papillae .............................................................................R. porosum

47. Organism parasitic on Pythium or Vampyrella......................................48
Organism parasitic on algae..................................................................49

48. Organism parasitic on Pythium................................................R. pythii
Organism parasitic on Vampyrella.........................................R. vampyrellae

49. Resting spore sexually formed................................................R. couchii
Resting spore asexually formed............................................................50

50. Resting spore 8-15 micrometers diameter, organism parasitic on Ulothrix..................................................................................R. karlingii
Resting spore 25-30 micrometers diameter, organism parasitic on a variety of algae..................................................................................R. globosum

51. Zoospores form a loose mass (but are not enclosed in a vesicle) at or outside discharge pore........................................................................52
Zoospores discharge singly or consecutively, but do not remain as a loose mass................................................................................................53

52. Sporangium 6-8 micrometers diameter, zoospores form a loose mass at the apical pore, attached to the pore by the tips of the flagella........................ .....................................................................................R. constantineani
Sporangium 12 micrometers diameter, zoospores form a loose mass outside the sub-apical or lateral pore...................................................R. algavorum

53. Discharge apparatus a single apical, subapical, or lateral pore................ .......................................................................................................54
Discharge apparatus 2-5 (rarely single) pores.........................................63

54. Discharge apparatus a single lateral pore.............................R. canterae
Discharge apparatus a single apical or subapical pore..............................55

55. Sporangium wall double-contoured...................................................56
Sporangium wall not double-contoured...................................................57

56. Organism saprophytic on pollen, rhizoid extensively branched.................. ...........................................................................................R. annulatum
Organism parasitic on Spirogyra, haustorium a short, blunt, peg-like tube ....................................................................................R. brevipes

57. Sporangium wall ornamented............................................................58
Sporangium wall smooth, not ornamented................................................59

58. Wall covered with conspicuous spines, rhizoids branched, organisms saprophytic on pollen.....................................................R. echinocystoides
Wall covered with short, sharp spines, haustorium a single, unbranched, slightly inflated tube, organism parasitic on Cladophora............R. spinulosum

59. Sporangium small, 5-7.6 micrometers diameter....................................60
Sporangium larger, 10-20 micrometers diameter........................................61

60. Sporangium 5.4-7.6 micrometers diameter, endobiotic part a small bulbous or discoid base of the sporangium, organism parasitic on Bumilleria ............................................................................R. bumilleriae
Sporangium 5-7 micrometers diameter, endobiotic part a sparse, tenuous rhizoid, organism parasitic on Mougeotia.................................R. mougeotiae

61. Wall of sporangium distinctly thickened on lower part to form a cup-like base...........................................................................................R. tenue
Wall of sporangium not thickened on lower part........................................62

62. Sporangium 10-15 micrometers diameter, rhizoid simple, filamentous, short; organism parasitic on Cladophora.................................R. cladophorae
Sporangium 16-20 micrometers diameter, rhizoid delicate, unbranched, short or up to 180 micrometers long; organism parasitic on Oscillatoria ...................................................R. oscillatoriae-rubescentis

63. Organism saprophytic on pollen........................................................64
Organism parasitic on various hosts.......................................................65

64. Sporangial wall smooth, single-layered, resting spore with an undulate outer wall...............................................................................R. undatum
Sporangial wall compound, outer wall a thin, undulating veil.......R. undulatum

65. Sporangial wall partially deliquesces prior to, or collapses after, zoospore discharge............................................................................................66
Sporangial wall remains intact after discharge..................................R. fugax

66. Sporangial wall deliquesces to form multiple openings ........................67
Sporangial wall collapses after discharge..................................R. cyclotellae

67. Quartets of zoospores formed within sporangium, sporangial wall deliquesces to form multiple openings; organism parasitic on Asterionella.........................................................................R. tetragenum
Zoospores not delineated in quartets; sporangial wall deliquesces to form one to three openings................................................................................68

68. Four-60 zoospores delineated, sporangial wall deliquesces to form one to three openings; organism parasitic on Eudorina..................R. contractophilum
Three-20 zoospores delineated, sporangial wall deliquesces to form 1-3 openings; organism parasitic on Fragilaria.................................R. fragilariae

69. Sporangial wall ruptures to release zoospores................R. chytriophagum
Sporangial wall partially or entirely deliquesces to release zoospores..........70

70. Sporangial wall partially deliquesces to form 1-3 openings..................... .............................................................................................R. dubium
Sporangial wall entirely deliquesces........................................................71

71.Sporangium small, 3.5-4.5 micrometers diameter; organism parasitic on Achnanthes......................................................................... R. achnanthis
Sporangium larger, 5-20 micrometers diameter..........................................72

72.Sporangium stalked, 11-18 micrometers diameter; organism parasitic on Melosira ...............................................................................R. melosirae
Sporangium sessile...............................................................................73

73. Sporangium 5-11 micrometers diameter, zoospores mature at liberation..... ...............................................................................................R. difficile
Sporangium 12-20 micrometers diameter, zoospores not fully delineated at liberation .....................................................................R. sphaerocystidis

 



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