Gingersrus Database Taxon ID 4111
OLD NAME: Costus erythrothyrsus
NEW NAME: Costus erythrothyrsus
NAME CHANGE NOTES:
FULL SCIENTIFIC NAME: Costus erythrothyrsus Loes.
STATUS : accepted
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Costus erythrothyrsus is an accepted species of neotropical Costus first described by Loesener in 1929 from a collection by Guntar Tessmann in 1924 in Peru near the Pongo de Manseriche where the Rio Santiago meets the Rio MaraÅ„on. His holotype was destroyed in Berlin but a copy in Geneva was chosen by Paul Maas as the lectotype.
Maas described the species as a plant growing from 1 to 3.5 meters tall with red to pink non-appendaged bracts and tubular flowers with red corolla and pink labellum. He distinguishes it from Costus spiralis by the abaxial orientatio of the flower vs. adaxial flowers in C. spiralis. He indicates that it usually flowers from a separate leafless shoot at the base but sometimes flowering terminally on leafy stems.
Costus erythrothyrsus is recorded in two widely separated regions with different climatic patterns, raising questions of whether two different species might be involved. One region includes French Guiana, Suriname, Guyana, and adjacent northern parts of Brazil where there is a short dry season in September and October. Here the the species flowers in the rainy season. The other region is predominantly in Amazonian areas of Peru and Brazil (including the locality of the original type collection by Tessman) where there is a less distinct dry season and the species appears to flower year round. There is also a narrow leaf form from Acre, Brazil that Dr. Maas is proposing as a new species to be called Costus douglasdalyi.
There is a plant in cultivation of unknown origin that is a very short form with thin stems and flowering either terminally or basally that has been included in this species. I have seen plants in Acre, Brazil far up the Rio Azul close the Peruvian border that I believe to be this species, but I really am not certain.
A partial phylogeny was completed by Eugenio Valderrama and his associates in the Chelsea Specht Lab at Cornell University and was published in the journal Frontiers in Plant Science in September 2022. Paul Maas' collection 9334 from French Guiana has been sampled for DNA and this single sample is in a separate clade in a lineage with Costus claviger which also occurs in the Guianas. No sampling has been done from the type locality or other Amazonian regions of Peru or Brazil to see if they are the same species.
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