Sisyrinchium rosulatum

Sisyrinchium rosulatum View in CoL vs. S. micranthum

Shinners (1962) stated for S. rosulatum that “most of its North American range has been attained more recently” than 1908, and reports that he frequently found it in 1961–1962 in eastern TX where it was rare in 1948. He boldly stated that “Its original home was nearly the same as that of S. exile , from southern Brazil to Argentina.” As for S. exile , he stated that “The original home of this now very widespread weed seems to have been in the region from southern Brazil to northern Argentina. Since 1820, at least, the name S. micranthum has been used [in South America] for the plant here discussed.” Thus, Shinners appears to be the first to 1) connect the U.S. plants of S. rosulatum / exile with the plants of South America, and 2) treat them as non-native to the U.S. More recently, Goldblatt and Manning (2008) stated: “It seems likely that the two or three annual species that occur in the southern United States are fairly recent introductions from South America and not native.”

The native range of Sisyrinchium micranthum is primarily South American: southern Brazil, Uruguay, northern Argentina, and eastern Paraguay ( Zuloaga et al. 2008). In addition, plants originally determined as S. iridifolium Kunth in northern South America have been included within S. micranthum by recent authors. Sisyrinchium micranthum has also been documented from Central America north to Chiapas, Mexico ( Henrich & Goldblatt 1994) and the West Indies ( Henrich & Goldblatt 1987). There are specimens at SERNEC ( SERNEC 2022, herbarium TEX) that extend the Mexican range to Coahuila and Nuevo Leon states, both of which border on Texas. All of the above are treated as natural occurrences by the authors.

As an alien or adventive plant, Sisyrinchium micranthum (including synonyms S. iridifolium , S. laxum ) has been documented from Australia, California, China, Fiji, Korea, Madagascar, Malaysia, New Guinea, New Zealand, South Africa, and Sri Lanka ( GBIF 2022). Yamaguchi and Hirai (1987) studied hybridization among color morphs of non-native S. rosulatum in Japan, “introduced from North America,” identification made by K. Hornberger. Of note, one of these variants was previously identified as S. iridifolium var. laxum (Otto) Maekewa , which is native to South America and now treated as a synonym of S. micranthum . Thus, Japanese alien plants apparently involved two “species.”

In the United States, Oliver and Lewis (1962) determined chromosome numbers for plants of “ S. laxum ” collected in Angelina and Nocogdoches counties, Texas; and plants of “ S. micranthum ” collected in Angelina, Hardin, and Trinity counties, Texas. Both represent the first reports of those two South American taxa in North America. To comply with North American nomenclatural concepts of the time, Shinners added an Editor’s Note (p. 43), stating that S. laxum = S. rosulatum and S. micranthum = S. exile , based on flower color. Here again, Shinners treats the North and South American entities as conspecific and non-native in the United States.

Clearly,there has been much confusion regarding the specific boundaries of the members of the S.rosulatum / micranthum complex. Keys and descriptions do not provide any real help, as mensural characters overlap greatly if not completely, flower color is duplicated in both North and South America, and fruit size and color overlap completely. Johnston (1938) stated: “In my key I have given the characters which usually serve to distinguish S. laxum from S. micranthumz … There are plants which present embarrassing combinations of characters…from the region of overlap…where hybridization may be expected.” Chauveau et al. (2011, p. 1299) stated: “The range recorded in the World Checklist of Iridaceae for S.micranthum was applied similarly to all morphotypes of the complex, because their respective ranges were impossible to determine accurately from the existing data.” Shin et al. (2016) stated: “Because of the morphological plasticity observed within S. micranthum and the lack of careful studies on S. rosulatum , the identification of the two species is often unclear and recent molecular studies suggested that both are a single species, i.e., S. micranthum .” Examples of the variation are shown in Fig. 16 View FIG .