On July 2, 1996, some plants of Juncus bufonius L. (Juncaceae) that were observed by me on a forest road in Espoo, Kalajärvi, appeared somewhat deviating. On a closer look, more occurrences of this plant were detected in similar habitats. After some work with the literature, these deviating plants turned out to represent J. minutulus (Albert & Jahand.) Prain, a close relative of J. bufonius. The species have different chromosome numbers; J. bufonius is at a higher ploidy level. Specimens of the plant were preserved and placed in the Botanical Museum (H) of the Finnish Museum of Natural History. J. minutulus was not been reported or apparently even noted in Finland before. The taxonomic position of this taxon has been debated but it is treated as an independent species e.g. by "Flora Europaea". In Sweden, J. minutulus is generally regarded as a species of its own and it has even been observed to be fairly common in most part of the country.
Since then I have made observations on this species group in the field and the herbarium. The character set that is given in the literature to separate the taxa requires some revision. Hence, I have summarized my experiences of the diagnostic differences between these two closely related species in the table below.
| Juncus bufonius s. str. | Juncus minutulus | |
| Overall colour of the plant | fairly dark greyish green | paler, partly yellowish green |
| Red colour at plant base | mostly absent | mostly present |
| Length of outer perianth segments | 4.5-6.5 mm | 2.5-4.5 mm |
| Outer perianth segments : capsule length | clearly longer | slightly longer |
| Number of stamens | mostly 6 (rarely 3) | mostly 3 (rarely 6) |
| Length of capsule | 3.5-4-5 mm | 2.2-3.2 mm |
| Colour of mature capsule | green or pale brown | pale to dark red (at apex, at least) |
| Maturation of individual plant (capsules) | slow | fast |
A few less distinct differences also exist: J. bufonius is generally taller, one-stemmed individuals are apparently infrequent, its stamens and anthers are larger, and the relation anther : filament is greater.
The phenology of J. minutulus is earlier than that of J. bufonius, an observation already made by the esteemed Czech botanist Josef Holub. But as can be seen in Fig. 1, this also applies to a single plant individual: in the former species it develops more hastily as the capsules develop and mature almost at once within the whole plant. In J. bufonius, the flowers and capsules within a plant are at clearly variable stages of maturing. Fig. 1 (below) shows this difference: in J. bufonius, there are always some flower buds and immature capsules at the tips of the stems and branches, while in J. minutulus the development and maturation of the capsules extends rapidly throughout the plant! This difference may result from the different pollination strategies of the species: according to the literature the flowers of J. bufonius are mainly chasmogamous while those of J. minutulus are cleistogamous (getting thus rapidly self-pollinated).
The habitat ecology of the species is rather similar. However, it appears that J. minutulus probably more often occurs in trampled habitats such as yards, sports arenas, paths, and small roads and tracks.
It is not always easy to distinguish between the species as (i) J. minutulus is rather variable and (ii) plants that appear intermediate between J. bufonius and J. minutulus are found every now and then. Most of these "difficult" plants possess well developed seeds while a few possess poorly developed ones. The specific delimitation clearly deserves further study. – See below for an additional note on the variability of this species group!
Fig. 1. Juncus bufonius s. str. (Finland, Tuusula, Kirkonkylä, 1997; one tuft to the left) and J. minutulus (Finland, Lohja, Vanhakylä, 1998; five plants to the right). – Image: Harri Harmaja (scanned from dried specimens).
Fig. 2. Juncus sp. (Finland, Lohja, Vanhakylä, 1998). – Image: Harri Harmaja (scanned from dried specimen). – These plants were growing intermixed with typical J. minutulus plants shown in Fig. 1. The habitat was a very moist cart track in rich woods. This morph mainly differs from J. minutulus in that the seeds tend to be slightly ovoid and their surface is beset with ca. 15-20 slightly elevated, longitudinal ridges that are brown (i.e., darker than the remainder surface). In J. minutulus, the seeds are ellipsoid with a surface comprising ca. 30-35 almost invisible, dense striae that do not contrast to the background in colour (both being very pale brownish).
Created May 25, 2003. Latest revision May 3, 2007.