Microbotryum Lév.

Type

Microbotryum antherarum (DC.) Lév. on Silene nutans L.

Description

Sori in various organs (mainly anthers) of the host plants in several dicotyledonous families. Spore mass dusty, light to dark purplish brown.

Spores solitary, pale to dark violet-brown; surface variously ornamented, often reticulate, also echinulate, verrucose or striate. Peridium globose; columella and capillitium-like threads absent in the sori.

Sterile cells absent between the spores.

Spore germination resulting in phragmobasidia with successive production of sessile basidiospores; sterigmata absent.

Host-parasite interaction by intercellular hyphae lacking interactions with deposits of specific fungal vesicles.

Septa poreless at maturity.

Comments

Moore (1996a, b) proposed that Microbotryum should be restricted to Ustilago-like species on Caryophyllaceae, with Bauhinus R.T.Moore including Ustilago-like species on Polygonaceae, Dipsacaceae and Compositae. Almaraz et al. (2002) considered that Microbotryum should be restricted to the anthericolous smuts on Caryophyllaceae based on DNA sequence analysis. Denchev et al. (2006) also considered that Microbotryum should be limited to anthericolous smuts on Caryophyllaceae and further established a new genus Haradaea Denchev for the seed-destroying species of Ustilago-like smuts on Caryophyllaceae.

For the present we retain Microbotryum sensu Vánky (1998, 2002) in the absence of reliable morphological characters that would allow its segregation into smaller genera. Microbotryum has c. 88 species infecting hosts in the Asteraceae, Caryophyllaceae, Dipsacaceae, Gentianaceae, Lamiaceae, Lentibulariaceae, Onagraceae, Polygonaceae, Portulacaceae and Primulaceae. Among the c. 24 species that infect hosts in the Caryophyllaceae, about 14 infect the anthers. Eight species of Microbotryum have been recorded in Australia, including one that has been eradicated and two that are endemic.

Species in Australia
 
Microbotryum calyptratae
Microbotryum dianthorum
Microbotryum dumosum
Microbotryum nivale
Microbotryum parlatorei
Microbotryum prostratum
Microbotryum reticulatum
Microbotryum tenuisporum

Key based on host taxonomy
 
On Caryophyllaceae1
1.  On DianthusMicrobotryum dianthorum
On SaginaMicrobotryum nivale
On Polygonaceae1
1.  On Rumex2
On Persicaria3
2.  Meshes 6-9 per spore diameter. Muri 0.5-0.8 µm highMicrobotryum dumosum
Meshes 5-8 per spore diameter. Muri 1-1.5 µm highMicrobotryum parlatorei
3.  Meshes (-2)3-4 per spore diameter. Muri 1-1.5 µm highMicrobotryum reticulatum
Meshes 3-5 per spore diameter. Muri lower4
4.  Muri 0.5-1 µm high. Interspaces irregularly wartyMicrobotryum prostratum
Muri 0.8-1.2 µm high. Interspaces nearly smoothMicrobotryum tenuisporum
On PortulacaceaeMicrobotryum calyptratae