Bull. Natn. Sci. Mus., Tokyo, Ser. B, 32(1), pp. 1–8, March 22, 2006

Dictyostelids in Japan. XIV. Dictyostelium rosarium Raper & Cavenderand Polysphondylium filamentosum Traub, Hohl & Cavender
Hiromitsu Hagiwara1 and Haruhiro Hosono2
1

Department of Botany, National Science Museum, Amakubo 4–1–1, Tsukuba, 305–0005 Japan
E-mail: h-hagiwa@kahaku.go.jp
2Kumagaya-nishi High School, Mikajiri 2066, Kumagaya, Saitama, 360–0843 Japan

Abstract Two species of dictyostelids, Dictyostelium rosarium and Polysphondylium filamentosum, were recovered in Japan. D. rosarium, characterized by sessile lateral sori and globose spores,
is reported after an absence of 35 years and is redescribed here in detail. P. filamentosum, characterized by the rebranching of whorled branches and the filamentous elongation of sorophores, isdescribed from indigenous Japanese material for the first time.
Key words : dictyostelids, cellular slime molds, Dictyostelium rosarium, Polysphondylium filamentosum, taxonomy, Japan.

Dictyostelium rosarium Raper & Cavender andPolysphondylium filamentosum Traub, Hohl &Cavender are among the most striking species ofdictyostelid cellular slime molds. D. rosarium,
first isolated from soil in Texas, USA and dung in
Mexico and Washington, USA (Raper & Cavender, 1968), is distinguished by a combination of
two characteristics, namely, sessile lateral soriand globose spores. Although widely distributed,
the species tends to be rare. An exception isNorth America, where it is locally common insome substrates and regions, for examples inmoderately dry or saline soils in southern California (Benson & Mahoney, 1977) and in soils
from bat caves in West Virginia (Landolt &Stephenson, 1991). In Japan, it was previously
known from only a single isolate taken fromdung at Tama Zoo, Tokyo (Lee, 1970). P. filamentosum, originally described from isolates obtained from the soils of deciduous and conifer
forests in Switzerland (Traub et al., 1981), ischaracterized by the rebranching of whorledbranches and the filamentous elongation of bothsorophores and branches. This species is commonly recovered in Switzerland and Germany(Cavender et al., 1995) and also in Hokkaido,
Japan (Cavender & Kawabe, 1989), but rarely inNorth America (Swanson et al., 1999).

In the course of this study on Japanese dictyostelids, D. rosarium and P. filamentosum wereobtained from Honshu, Japan. Although bothspecies have been previously reported fromJapan (Lee, 1971; Cavender & Kawabe, 1989),
these indigenous dictyostelids have neither been
cultured nor observed by the methods followed in
the present study. Descriptions of and observational notes on these species are presented here.
The procedures of isolation, cultivation, andobservation were the same as those reported previously (Hagiwara, 1989). All the isolates examined were cultured at 20°C on non-nutrient agar
with Escherichia coli. The technical terms used
to describe Polysphondylium followed those in
Harper (1929); that is, a point on the sorophorefrom which a whorl of branches grows out of istermed a “node”; a segment between nodes on
the sorophore, an “internode”; and a portion of
the sorophore above the uppermost node, the“terminal segment.” The abbreviations relating to
the morphology and dimensions of sorocarps are
as follows:
B: Number of branches per whorl.
BB(max): Width of a branch base at the thickest point (m m).
BL: Branch length (m m).
MD: Mean size of spores per isolate (m m).

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Hiromitsu Hagiwara and Haruhiro Hosono

Fig. 1. Dictyostelium rosarium. A. Sorophore tips. B. Sorophore bases. C. Sorophore base surrounded by manyvacuolated cells. D. Supporter.

N: Number of whorls per sorocarp.
SLL: Length of a sorophore with a lengthened
terminal segment (m m).
STL: Width of a lengthened terminal segment
at a level 50 m m below the apex (m m).
TLL: Length of a lengthened terminal segment(m m).
Dictyostelium rosarium Raper & Cavender,
J. Elisha Mitchell Sci. Soc., 84: 31 (1968).
(Figs. 1 & 2)
Sorocarps usually solitary but sometimes clustered, sometimes sparsely and irregularly
branched, often prostrate. Sorophores colorless,
0.8–6.2m m in length, sometimes exceeding 8m m

if prostrate, with 3–7 sessile lateral sori, sometimes with supporters if prostrate (Figs. 1D &2H); bases acuminate or clavate (Figs. 1B & 2G),
16–24 m m in diam at thickest point; tips obtuse,
simple to compound (Figs. 1A & 2F), 6–16 m m
in diam at a level 50 m m below the apex. Soriwhite, globose to subglobose; terminal sori
40–290 m m in diam; lateral sori 30–260 m m indiam. Spores hyaline, globose, smooth, mostly
4.9–5.6 (MD: 5.3) m m in diam. Pseudoplasmodia
radial (Fig. 2A), 0.5–23 mm in diam, centralized,
not migrating without sorophore formation,
sometimes producing plural sorogens.
Habitat: On dung and in field soil.

Dictyostelids in Japan. XIV.

Fig. 2. Dictyostelium rosarium. A. Pseudoplasmodium. 12. B. Nodules produced in the process of aggregation. 12. C. Sorogen arising from a single aggregation. 28. D. Part of an immature sorocarp. 28. E. Lateral sessile sori along sorophores. 20. F. Sorophore tip partially surrounded by slime materials. 460. G.
Sorophore base accompanying vacuolated cells. 460. H. Supporter. 460. I. Spores. 1150. All figs.,
Strain S-12.

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4Hiromitsu Hagiwara and Haruhiro Hosono

Isolate examined: S-12, from a field soil at ca.
60 m alt. in the suburbs of Fukaya-shi, SaitamaPref., 8 July 2005.
Distribution: Asia; Japan, Pakistan. N. America; Mexico, USA. Oceania; New Zealand.
Dictyostelium rosarium is easily distinguishedfrom other dictyostelids by two characteristics,
namely, its globose spores (Fig. 2I) and sessile
sori borne at intervals along the uprightsorophore (Fig. 2D & 2E).
As a third distinguishing characteristic of D.
rosarium, Cavender et al. (2002) added the nodular aggregation pattern. Japanese isolate S-12
produced typical nodules during the inflow ofmyxamoebae into an aggregation center (Fig.
2B). In a moderate pseudoplasmodium, suchnodules eventually flowed into the aggregation
center and yielded a single sorocarp (Fig. 2C).
Dictyostelium rosarium is known to be widelydistributed and common in North America(Raper, 1984). Cavender et al. (2002) found thisspecies in New Zealand and confirmed that D.
rosarium is scattered not only in the Northern
Hemisphere but also in the Southern Hemisphere. In Japan, this species was first obtained
from wallaby dung at Tama Zoo, Tokyo in 1970
(Lee, 1971). A second Japanese isolate was recovered in this study after an absence of 35years. D. rosarium seems to be quite rare inJapan.
Polysphondylium filamentosum Traub, Hohl& Cavender, Amer. J. Bot., 68: 169 (1981).
(Figs. 3–5)
Sorocarps usually solitary but sometimes clustered, with 1–4 nodes, with 2–14 branches perwhorl, often with conspicuously lengthened terminal segments (Fig. 4G), sometimes prostrate.
Sorophores colorless, stout, 1.1–2.3 (SLL3.5–10.4) mm in length; bases robust, usuallyround (Figs. 3B & 5E), 22–68 m m in diam at thethickest point; tips acuminate (Figs. 3A & 5A),
sometimes nearly obtuse if lengthened (Figs. 3C& 5B), simple, 3.6–9.6 (STL 3.2–8) m m in diamat a level 50 m m below the apex; terminal segments 231–462 (TLL 2000–5600) m m in length;
internode segments 436–559 (–1103) m m inlength. Branches colorless, stout, 255–627 m min length, sometimes rebranching (Figs. 3F, 4E,4F & 4I), sometimes producing filamentously
lengthened tips; bases round, 11–40 m m in diamat the thickest point; tips acuminate (Figs. 3D &5C), sometimes nearly obtuse if lengthened (Fig.
3E), simple. Sori white, globose; terminal sori
42–106 (–127) m m in diam, diminishing to almost zero if tips are lengthened; lateral sori
42–106 m m in diam. Spores hyaline, elliptical toslightly reniform, usually 2.0–2.4 times longer
than broad, smooth, mostly 8.4–10.73.9–5.0(MD: 9.2–9.94.1–4.7) m m, with conspicuous
unconsolidated polar granules (Fig. 5G). Pseudoplasmodia radial (Fig. 4A), 0.15–6.5 (–8.5) mmin diam, centralized, not migrating withoutsorophore formation.
Habitat: In forest soil.
Isolates examined: CSB6, from soil of a deciduous forests at ca. 30 m alt., Boso Fudoki-nooka, Chiba Pref., 2 July 1996; NYA55 & NYA65,
from the soil of larch forests, 1300–1600 m alt.,
the Yatsugatake Mts., Nagano Pref., 8 May 2005.
Index values of sorocarp dimensions
N: 2.30.5 (n52)
B: 5.32.3 (n173)
BL: 434100 (n57)
BB(max): 26.36.5 (n57)
Distribution: Asia; Japan. Europe; Germany,
Switzerland. N. America; USA.
Polysphondylium filamentosum is characterized by very long filamentous terminal segmentsof the sorophores (Fig. 4G), the rebranching ofwhorled branches (Fig. 4F), and the fairly large
elliptical spores with conspicuous, unconsolidated polar granules (Fig. 5G).
Polysphondylium filamentosum is easily distinguished from P. pallidum Olive, the most common species among white Polysphondylia, by its
elongated terminal segments of the sorophores.
Such an elongation has been reported in P. candidum Hagiwara (Hagiwara, 1973) and P. psedocandidum Hagiwara (Hagiwara, 1979). P. candidum closely resembles P. filamentosum not only
in morphological features but also in habitat,
and therefore, both the species are fairly difficultDictyostelids in Japan. XIV.

5Fig. 3. Polysphondylium filamentosum. A. Sorophore tips. B. Sorophore bases. C. Lengthened sorophore tips.
D. Branch tips. E. Lengthened branch tip. F. Branch with two secondary branches (branchlets).

to distinguish from each other. In P. candidum,
however, the rebranching that characterizes
P. filamentosum has not been reported. In addition,
P. candidum exhibits a well-defined regularbranching pattern with uniform branch lengths
and uniform sorus size per whorl. In P. pseudocandidum,rebranchinghasnotbeenreported. This subtropical species is easily distinguished from P. filamentosum by its delicate
sorocarps with small spores.
The pseudoplasmodia of the isolates examined

typically had radial aggregation (Fig. 4A). Undercertain conditions, however, many pseudoplasmodia were produced in a narrow area and theirradial streams often anastomosed with each other(Fig. 4B). In other conditions, a large pseudoplasmodium yielded several satellite secondaryaggregation centers and/or plural sorogens at theprimary aggregation center (Fig. 4C). Such alarge pseudoplasmodium often accompaniedring-like pseudoplasmodia with a vortex motion(Fig. 4D).

6Hiromitsu Hagiwara and Haruhiro Hosono

Fig. 4. Polysphondylium filamentosum. A. Pseudoplasmodium. 28. B. Pseudoplasmodia developed in a narrow area. Their radial streams often anastomose each other. 28. C. Sorogens irregularly produced at thecenter of a large aggregation. 28. D. Ring-like pseudoplasmodia. Their streams flow like the vortex. 28.
E. Rebranching of whorled branches. 28. F. Whorled branches with secondary branches (branchlets). 20.
G. Lengthened terminal segment of a sorophore. 20. H. Growth habit. 8. I. Two branches with whorls ofbranchlets. 115. Figs. B, F, H & I, strain CSB6; Figs. C-E, strain NYA55; Figs. A & G, strain NYA65.

Dictyostelids in Japan. XIV.

7Fig. 5. Polysphondylium filamentosum. A. Tip of a sorophore. 460. B. Tip of a lengthened sorophore. 460.
C. Tip of a branch. 460. D. Tip of a branchlet. 460. E. Sorophore base. 460. F. Hook-like structure of aprostrate sorophore at the point of contact with agar. 460. G. Spores. 1150. Figs. A & D, strain CSB6;
Fig. E, strain NYA55; Figs. B, C, F & G, strain NYA65.

Branches were usually stout or heavy at theirbases and often longer than the unlengthened terminal segments of sorophores. The branch lengthand sorus size per whorl exhibited some degreeof variation (Fig. 4H). Additionally, the branching angles from the sorophores were also variable. The observed variability could be attributed
to the disproportionately large size of branchbases as compared with the thickness of thesorophore attached to the branches.
Rebranching is an important taxonomic criterion of P. filamentosum. Such a phenomenon isconspicuous in cultures grown on 0.1 LP agar
(Traub et al., 1981); however, it is not accentuated on non-nutrient agar even though terminal
segments are often lengthened (Fig. 6).
Finally, it is noteworthy that prostrate sorocarps produced hook-like structures at the pointof contact with agar (Fig. 5F). Such structures

have been observed in both D. rizopodium Raper& Fennell and D. vinaceo-fuscum Raper & Fennell (Raper & Fennell, 1967), and also in D. aureocephalum Hagiwara (Hagiwara, 1991, 1998);
however, they have not been seen in Polysphondylia.
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