Gingersrus Database Taxon ID 3310Dimerocostus argenteusOLD NAME: Dimerocostus argenteus NEW NAME: Dimerocostus argenteus NAME CHANGE NOTES: FULL SCIENTIFIC NAME: Dimerocostus argenteus (Ruiz & Pav.) Maas STATUS : accepted CONTINENT: Neotropical FIELD OBSERVATIONS:(If field observations are available, you can click on the link to open in a new window.) FIELD OBSERVATIONS PHOTOS:(If photos are available, you can click on the link to open in a new window.) GOOGLE PHOTO ALBUM SYNONYMS: - Costus argenteus Ruiz & Pav. (1798) - Dimerocostus gutierrezii Kuntze (1898) - Dimerocostus strobilaceus Kuntze subsp. gutierrezii (Kuntze) Maas (1972) - Costus mooreanus Rusby (1907) - Mulfordia boliviana Rusby (1928) - Dimerocostus bicolor J.F.Macbr. (1930) BOTANICAL NOTES: Dimerocostus argenteus is an accepted species of Dimerocostus, first collected and described as Costus argenteus by Ruiz & Pavon in the late 1700's. The type specimen was collected at a place called Chinchao in present-day Department Huanuco, Peru in 1778. Ruiz described it 20 years later in 1798 in his Flora Peruviana. In 2016 I visited Chinchao and found the species still growing there, and I photographed it there. My field observations can be found at the link above. In 2016 I visited Chinchao and found the species still growing there, and I photographed it there. My field observations can be found at the link above. D. argenteus is distinguished from other Dimerocostus species by the silvery undersides of the leaves, for which it is named. It is also one of the species of Dimerocostus that produces bract appendages, but the appendages are not persistent, but soon decay and often leave a plant that looks to be non-appendaged. In some plants the upper bract appendages are still intact but the lower ones are decayed. The other distinctive character of D. argenteus is the flower shape, with a small labellum whose edges are curled and with a long upper corolla lobe that forms a hood. The flowers are usually pale yellow in color. During my field observations of many plants of this species, I found that there is a great deal of variation. Many of the plants, expecially at lower elevations, tend to have a ring of long stiff hairs around the ligules. In some plants the bract appendages are almost completely gone, but in others they they are large and persistent. In the past this species has been confused with the Dimerocostus found in southern Bolivia that were previously known as Dimerocostus strobilaceus subspecies gutierrezii, first collected by Otto Kuntz in 1892 and described in 1898 as Dimerocostus gutierrezii. I visited the type locality of this Kuntz collection in 2017 and discovered that all the Dimerocostus in that region had silvery undersides to the leaves and produced a hooded flower form with a small labellum. The type specimen was very poor and had been misinterpreted, so that species gutierrezii (and the subspecies gutierrezii) are now considered to be synonyms of D. argenteus. The primary difference I found in the plants growing in southern Bolivia was that the upper bracts were large and persistent. I have also found that the silvery undersides of the leaves are always present in this species and that there is still room for confusion between this species and Dimerocostus rurrenabaqueanus (the name that replaced Dimerocostus strobilaceus subspecies gutierrezii. A molecular phylogeny in 2020 at Cornell University included 12 samples from Dimerocostus including two presumed D. argenteus - one from the type locality in Peru and the other from southern Bolivia near the type locality of D. gutierrezii. It was found that the two samples were in separate well-supported clades, but in very close lineages and well separated from the other presumed species. Whether these various forms should be split into separate taxa is a question for future research.
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