Costus laevis

• Changes to Costus guanaiensis
• Changes to Costus laevis.

It is proposed for publication in 2022 to split the current Costus guanaiensis var. tarmicus into two separate species. The plants that are in the form of the original Costus tarmicus Loesener will be changed to Costus laevis Ruiz & Pav. because it's publication pre-dates Loesener's publication. There is another group of plants, mostly from western Ecuador, that currently are considered part of Costus guanaiensis var. tarmicus, but will be split from tarmicus and published as a sp. nov. Costus gibossus.

The former Costus guanaiensis var. tarmicus was described in 1972 by Paul Maas as part of his monograph on neotropical Costaceae. He distinguished that form from the others by the indumenta on the leaves and sheaths being glabrous or only sparsely puberbulous vs. the more densely hairy leaves and sheaths of the other varieties. The variety was based upon the type specimen for Costus tarmicus Loesener, collected by A. Weberbauer in 1901 near La Merced in the province of Tarma, department Junín, Peru.

In December 2017 I traveled there to search for both this species and also for Costus weberbaueri. There and in adjacent department Pasco, I found this to be a very common species, quite consistent in the form of the inflorescence, but quite variable in terms of hairiness of the leaves and sheaths. It also became clear to me that the type for this species is completely different from the plants found in western Ecuador with the horizontal bract appendages and bulges in the basal parts of the sheaths at the margins. I prepared an analysis sheet of the various forms of bract appendages and hairiness for the plants that are currently considered this variety and Dr. Maas agreed that the species needed to be split between the plants of western Ecuador and those in the region of the type specimen in Peru.

After much study and after splitting out the Costus sp. nov. gibbosus, Dr. Maas prepared the following description to distinguish this "tarmicus" form (now to be named Costus laevis) from the others: "Costus tarmicus occurs all over western South America, from Colombia to Peru (PM doubts if the one collection from Venezuela also belongs here). It is marked by bracts which have weakly developed, green appendages. Another feature of this species is the often absence of any indument. There are, however, quite a few exceptions to this rule as the sheaths and/or the lower side of the leaves can be sparsely to densely puberulous to villose. An example of a dense indument is C. tarapotensis, which looks quite similar to typical C. tarmicus but which has the lower side of the leaves densely villose. As in all the three species of the former “Costus guanaiensis-group” (C. macrostrobilus, C. sinningiiflorus, and C. tarmicus) much additional work is needed to find out if more species are involved."

We also debated the status of the species Costus tarapotensis Macbride. It has a very similar inflorescence, with similar triangular bract appendages and similar flower to the plants found in the C. tarmicus type locality, but specimens generally are densely covered with soft white hairs, differing from the typical tarmicus (now laevis) plants. NOTE: In my opinion, Costus tarapotensis has other differences and should be considered a good species, separate from Costus laevis. More about that on the page for Costus tarapotensis 'Morning Star'.

In summary, the "new" Costus laevis has green, erect, triangular shaped, appendaged bracts, or triangular shaped bracts that look somewhat like appendages. The flowers are always terminal on a leafy stem, are erect or abaxially oriented with respect to the bracts, and form a long and broad tube with a spreading labelum that has red stripes. The corolla is usually white but some plants that have been placed within this species are found with yellow or even orange bracts. The plants I have seen that best fit into this species are found from the far south of Ecuador to central Peru along the eastern flanks of the Andes at elevations from about 500 to 1700 meters.

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. DNA has been extracted from several samples of this species but results have not yet been compiled in the phylogeny.

HORTICULTURAL NOTES:
This species has been in cultivation in botanical gardens in Hawaii and from there has been widely distributed. I misinterpreted it and listed it as Costus aff. claviger before I visited the type locality in Peru. It seems to have originated in the National Tropical Botanical Garden, their number 72S734, received from Robert Wilson, No. 65-346, original collection in Peru, probably Tingo Maria area. It is also grown in Waimea Arboretum as No. 74P389 and at Lyon Arboretum as 800705. I have even seen it cultivated in a private garden on the island of Borneo!

I have also now determined that the cultivar I registered as Costus 'Marco's Pride' from soutern Ecuador belongs in this species.

ACCESSIONS:Click links (if any) to see details of individual collections. R3000- R3008- R3259- R3327- R3329- R3330- R3375- R3379- R3412- R3413- R3414- R3543-

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