Bull. Natn. Sci. Mus., Tokyo, Ser. B, 22(2) , pp. 47- 54, June 22, 1996

Dictyostelids in Japan. X*. Two New Species of Dictyostelium,
D. pseudo-brefeldianum and D. robustum
By

Hiromitsu HAGIW ARA
Department of Botany, National Science Museum,4- 1- 1 Amakubo, Tsukuba, lbaraki 305, Japan
Abstract Two new species of dictyostelids, Dictyostelium pseudo-brefeldianum andD. robustum, are described based on isolates from forest soils in the temperate regionsof Japan. Dictyostelium pseudo-brefeldianum is characterized by large but slendersorocarps, white sori, clavate sorophore tips, and elliptical spores without polar
granules. Dictyostelium robustum is characterized by large and very robust sorocarps,
white sori, somewhat capitate or nearly simple sorophore tips, and elliptical spores
without polar granules.

In the course of my studies on Japanese dictyostelids, two new species ofDictyostelium were obtained. The descriptions and some observations on these
species are presented here.
Procedures of isolation, cultivation and observation are the same as thosereported previously (Hagiwara, 1989) . Type specimens are preserved in theherbarium of the National Science Museum, Tokyo (TNS). Subcultures from thetype isolates are kept in the American Type Culture Collection, Maryland, U.S.A.
Dictyostelium pseudo-brefeldianum Hagiwara, sp. nov.
(Figs. 1 & 2)
Cultum ad 20°C in agaro non-nutricio cum Eschericia coli, sorocarpiis

p1erumque solitaris, interdum gregariis, non vel pauco ramosis, phototropicis,
saepe prostratis; sorophoreis tenuibus, hyalinis, aliquantum sinuosis, l.o-7.9(- 20.8) mm longis, e basibus di1atatis oriundis, gradatim attenuatis, cum apicibus
clavatis, prope basem 7-27(- 33) .urn crassis, prope apiceum 2.5-10(-17.5) .urn
crassis; saris albis, globosis, 2o-300(-350) .urn in diam; sporis hyalinis,
ellipsoideis, plerumque 1.6-2.2-plo longioribus quam latioribus, levibus,
p1erumque 6.o-8.4 X 3.1-4.3 .urn, sine polaribus granulis; pseudoplasmodiis
radiatis, 0.6-4.4 mm in diam, plerumque sola sorocarpia producentibus.
When cultured at 20°C on non-nutrient agar with Eschericia coli, sorocarps* The title was changed from "The Acrasiales in Japan" because dictyostelids or dictyostelid
cellular slime molds, which were treated under this title, are not included in the order Acrasiales
at present (Hawksworth et al. , 1995). IX : Bull. Natn. Sci. Mus., Tokyo, Ser. B, 12: 99-105,1986.

48

Hiromitsu HAGIWARA

usually solitary, sometimes gregarious, usually unbranched, sometimes sparsely
and irregularly branched, phototropic, often prostrate; sorophores slender, colorless, sinuous, l.G-7. 9 mm in length, sometimes exceeding 20 mm if prostrate,
gradually tapering from conical bases to clavate tips (Figs. lA & 2C-E), usuallysurrounded by basal disks (Figs. lB & 2F), usually consisting of a single tier ofcells in a large portion except for both terminal parts, 7- 27(- 33) f1m in diam at alevel 100 f1m above the bottom, 2.5- 10(-17.5) flm in diam at a level 50 flm below
the top; basal disks small, 15- 40(- 80) f1m in diam; sori white, globose, 2G-300(-350) f1m in diam; spores hyaline, ellipsoid, usually 1.6- 2.2 times longer thanbroad, smooth, mostly 6.G-8.4 X 3.1-4.3 (MD* 6.5-7.7 X 3.4-4.0) f1m, without
polar granules; pseudoplasmodia with definite radiate streams (Fig. 2A), 0.6- 4.4
mm in diam, often migrating with sorophore formation, usually producing single
sorogens.
Habitat: In humus and fermentation layers of forest soil in the temperateregions of Japan.
Isolates examined: Ha-3, 4, 9, 11, 12, 19, 24 and 25, 8Q0-1080m alt. , coniferous forests, Mt.
Hayachine-san, Iwate Pref. , Aug. 1979; MA-6, 8, 21 , 25, 42 and 44, 145Q--2000m alt. , deciduous andconiferous forests, Mt. Shiomi-dake, Nagano Pref., Aug. 1979; IY-11 , 13, 31 , 46, 53, 78, 83, 115 and116, 5Q--840m a1t. , deciduous forests, Mito to Mt. Yamizo-san, lbaraki Pref., Aug. 1994.

Type specimen: M-50024 (TNS), ex IY-78.

Fig. I.

Dictyostelium pseudo-brefeldianum. A. Sorophore tips. B. Sorophore bases. Bar =IO,um.

* Range of mean spore diameters of the isolates examined.

Dictyostelids in Japan. X.

Fig. 2.

Dictyostelium pseudo-bref eldianum.

A. Pseudoplasmodium. X 12.

49

B: Spores.

X 1200. C- E. Sorophore tips. X 480. F. Sorophore base. X 480.

Dictyostelium pseudo-brefeldianum is characterized by large but slender
sorocarps, white sori, clavate sorophore tips, and elliptical spores without polar
granules. According to the terminology in Hagiwara ( 1989), its sorophores are"gigantic" in length, and its sorophore tips may be "simple" and "capitate" in theproper sense because most of them become suddenly thicker than in any otherpart of the upper sorophores near the top (Fig. lA). Its spores are not oblong but
elliptical in shape, viz., their sides are not parallel but curved (Fig. 2B) .
Dictyostelium pseudo-brefeldianum fits well the species concept of D. mucoroides Brefeld emended by Raper (1984) . However, I believe that Raper'semendation of D. mucoroides deviates from Brefeld's original description andillustration, which was indicated by Hagiwara (1984a) , and moreover Raper'sspecies concept of D. mucoroides is too broad including seven or more morphologically distinct groups I recognize as separate species such as D. arabicum
Hagiwara, D. brefeldianum Hagiwara, D. clavatum Hagiwara, D. .firmibasis
Hagiwara, D. implicatum Hagiwara, D. longosporum Hagiwara and D. medium

'-"
0Table I.

Comparison of some morphological features among Dictyostelium pseudo-brefeldianum and its related species.*
SporesSorophores

D. pseudo-brefeldianum
D. arabicum
D. brefeldianum
D. clavatum
D. firmibasis
D. implicatum
D. longosporum
D. medium

References

Length**Width ofbases***

Shape of tips

Shape

Size (MD, tLm)

large to gigantic
large
large
large
gigantic
large
large
large

thin
thick
thin
moderatethickmoderate
moderate
moderate

simple to compound, clavatecompound, clavate
simple, typically capitate
compound, clavate
simple, somewhat capitate
simple, acuminate
simple, typically capitate
simple, somewhat capitate

ellipticaloblongoblongoblongellipticalellipticalellipticalelliptical

6.5- 7.7 X 3.4-4.0
6.3-6.9 X 3.6--3.9
5.9-6.7 X 3.3- 3.7
5.4-5 .5 X 2.9-3.1
6.9-8.4 X 2.9-3.6
7.4- 8.4 X 4.o-4.8
7.4-8.2 X 3.3- 3.6
6.4- 7.0 X 3.4- 3.7

Hagiwara (1991)
Hagiwara (1984a, 1989)
Hagiwara ( 1992)
Hagiwara ( 1989)
Hagiwara ( 1989)
Hagiwara (1983)
Hagiwara ( 1992):z::a·~·"'c:z::)>Table 2.

Cl

Comparison of some morphological features among Dictyostelium robustum and its related species.*
Sorophores~)>

SporesReferences

D. robustum
D. firmibasis
D. giganteum ( = D. magnum)
D. septentrionalisWidth of bases***

Shape of tips

ShapeSize (MD, tLm)very thick
thickmoderate
thick

simple, somewhat capitate
simple, somewhat capitate
simple, somewhat capitate
compound, typically capitate

ellipticalellipticaloblongelliptical

7.7- 8.8 X 3.4- 4.1
6.9-8.4 X 2.9-3.6
6.5- 7.4 X 3.6--4.2
8.4- 9.5 X 4.5- 5.6

Hagiwara (1989)
Hagiwara (1983)
Hagiwara ( 1989)* Small sorocarps and prostrate ones in each species were excluded in the comparisons.
** Categories of the sorophore length follow Hagiwara (1989), viz., the sorophores usually exceeding 3.5 mm but not or rarely more than
6 mm are "large", and ones often or usually exceeding 6 mm are "gigantic".
*** Sorophore bases are tentatively grouped into five categories, "very thin", "thin", "moderate", "thick" and "very thick", which indicate
the sorophore bases at 100 tLm above the bottom not or rarely exceeding 10 tLm , 30 tLm, 50 tLm, 70 tLm and more in width, respectively.

~

Dictyostelids in Japan. X.

51Hagiwara. Therefore, I cannot accept Raper's concept of D. mucoroides although
it is widely accepted.
Dictyostelium pseudo-brefeldianum is macroscopically similar to D. brefeldianum in the outline of sorocarps except for somewhat longer sorophores, therefore it is difficult to distinguish between the two species under a dissecting
microscope. But the new species is easily distinguished microscopically from D.
brefeldianum by clavate sorophore tips and elliptical and somewhat larger spores.
Also from other related species, the present species is distinguished by thecombination of dimensions of sorophores, shape of sorophore tips, and size andshape of spores (Table 1) .
Dictyostelium robustum Hagiwara, sp. nov.

(Figs. 3 & 4)
Cultum ad 20°C in agaro non-nutricio cum Eschericia coli, sorocarpiis
plerumque solitaris, interdum gregariis, non vel pauco ramosis, phototropicis,
interdum prostratis; sorophoreis robustis, hyalinis, aliquantum sinuosis, 0.4- 11.6mm longis, e basibus dilatatis oriundis, gradatim attenuatis, cum apicibus
aliquantum capitatis, prope basem 5- 114 ,urn crassis, prope apiceum 2-12 ,urncrassis; saris albis, globosis, SG-400(- 640) ,urn in diam; sporis hyalinis,ellipsoideis, plerumque 1.9-2.6-plo longioribus quam latioribus, levibus,
plerumque 7.1- 9.6 X 3.2- 4.4 ,urn, sine polaribus granulis; pseudoplasmodiis
radiatis, 0.3- 6.8(-8.0) mm in diam, plerumque sola sorocarpia producentibus.
When cultured at 20°C on non-nutrient agar with Eschericia coli, sorocarps
usually solitary, sometimes gregarious, usually unbranched, sometimes sparsely
and irregularly branched, phototropic, sometimes prostrate; sorophores robust,colorless, sinuous, 0.4-11.6 mm in length, gradually tapering from conical, roundor clavate bases (Figs. 3B-D & 4D, E) to somewhat capitate or nearly simple tips
(Figs. 3A & 4C), sometimes with supporting cells and supporters, often
surrounded by basal disks, 5-114 ,urn in diam at a level 100 ,urn above the bottom,
2-12 ,urn in diam at a level 50 ,urn below the top; basal disks 45-180 ,urn in diam,sometimes well-developed and 205- 650 ,urn in diam; sari white, globose, SG-400(-640) ,urn in diam; spores hyaline, ellipsoid, usually 1.9- 2.6 times longer thanbroad, smooth, mostly 7.1-9.6 X 3.2- 4.4 (MD 7.7-8.8 X 3.4-4.1),um, without
polar granules; pseudoplasmodia with definite radiate streams (Fig. 4A), 0.3-6.8(-8.0) mm in diam, rarely migrating without sorophore formation, usually
producing single sorogens.
Habitat: In humus and fermentation layers of forest soil in the temperateregions of Japan.
Isolates examined: Ha-! , 6, 9, 14, 22 and 23, 78<r-1020m alt., coniferous forests, Mt.
Hayachine-san, Iwate Pref., Aug. 1979; Ch-37, 45, 48 and 53, 122<r-1380m alt. , deciduous forests,Mt. Chokai-san, Akita Pref. , Sept. 1983, reported as "Dictyostelium firmibasis variant" in Hagiwara(1984b); MB-2, 1050m alt. , deciduous forest, Mt. Haku-san, Ishikawa Pref., Sept. 1985; IY-52, 78,

52

Hiromitsu HAGIWARA

8Fig. 3. Dictyostelium robustum. A. Sorophore tips. B. Sorophore bases. C. Sorophorebase with supporting cells (arrow). D. Sorophore tip and base of a small sorocarp.
Bar = !Ot.tm for A, C, D and 20t.tm for B.

Fig. 4. Dictyostelium robustum. A. Pseudoplasmodium. X 12. B. Spores. X 1200. C.
Sorophore tip. X 480. D, E. Sorophore bases. X 120. F. Well-developed basal disk in
the isolate Ch-45. X 120. G. Part of a sorophore with a supporter (arrow). X 480. H.
Migration without sorophore formation in Ch-53 . X 12. I. Short and robust sorocarps
inCh-53 . X 12.

Dictyostelids in Japan. X.

Fig. 4.

53

54

Hiromitsu HAGIWARA

87, 95, 103, 115 and 130, lOQ--1000 malt., deciduous forests, Mito to Mt. Yamizo-san, Ibaraki Pref.,Aug. 1994.

Type specimen: M-50025 (TNS), ex Ch-53.
Dictyostelium robustum is macroscopically characterized by very large androbust sorocarps with white sori. Its elliptical spores don't have polar granules(Fig. 4B) . This new species is similar to three described species, D. firmibasis, D.
giganteum Singh and D. septentrionalis Cavender, in the size of sorocarps. Whenmorphological features are compared among the four species (Table 2), the newspecies is the most similar to D. firmibasis. However, D. robustum is different
from D. firmibasis in having longer sorophores with much thicker bases andsomewhat larger spores. It is not difficult to distinguish the two species under adissecting microscope because D. robustum sparsely produces much more robust
sorocarps than those of D. firmibasis though its small sorocarps (Fig. 3D)
apparently resemble medium-sized ones of the latter species.
The following respects are noteworthy. 1) Although basal disks were small
in general, quite large disks were sometimes produced in some isolates (Fig. 4F),
viz., 250 and 365 flm in the isolate Ch-45, 205 and 350 urn in Ch-48, 650 flm in
MB-2, and 260 and 470 flm in IY -130. 2) Pseudoplasmodia sometimes migrated
with sorophore formation, but most of the pseudoplasmodia stood up after
migrating a short distance and often produced supporters under the sorophores atthe standing point (Fig. 4G). 3) Pseudoplasmodia sometimes migrated a shortdistance without sorophore formation inCh-53 (Fig. 4H). 4) A few small but
robust sorocarps were produced from single pseudoplasmodia under unknown
conditions in Ch-53 (Fig. 41).

References
Hagiwara, H. , 1983. Four new species of dictyostelid cellular slime molds from Nepal. Bull. Natn.
Sci. Mus., Tokyo, Ser. B, 9: 149- 158.
Hagiwara, H ., 1984a. Review of Dictyostelium mucoroides Brefeld and D. sphaerocepha/um (Oud.)
Sacc. et March. Bull. Natn. Sci. Mus., Tokyo, Ser. B, 10: 27- 41.
Hagiwara, H ., 1984b. Altitudinal distribution of dictyostelid cellular slime molds in Mt. Chokai,Northern Honshu, Japan. Mem. Natn. Sci. Mus., Tokyo, (17) : 47- 54 (in Japanese).
Hagiwara, H., 1989. The Taxonomic Study of Japanese Dictyostelid Cellular Slime Molds. 131 pp.
National Science Museum, Tokyo.
Hagiwara, H., 1991. A new species and some new records of dictyostelid cellular slime molds fromOman. Bull. Natn. Sci. Mus., Tokyo, Ser. B, 17: 109-121.
Hagiwara, H ., 1992. Dictyostelium clavatum sp. nov. and Dictyostelium medium sp. nov.: new
dictyostelid cellular slime molds from Nepal. Bull. Natn. Sci. Mus., Tokyo, Ser. B, 18: 1--ti.
Hawksworth, D. L., P. M. Kirk, B. C. Sutton & D. N . Pegler, 1995. Ainsworth & Bisby's Dictionaryof the Fungi. 8th ed. 616 pp. CAB International, Oxon.
Raper, K ., 1984. The Dictyostelids. 453 pp. Princeton University Press, Princeton.