This page contains photos and description of a species, form or cultivar of Costaceae.

Gingersrus Database Taxon ID 4035

Costus comosus


OLD NAME: Costus comosus

NEW NAME: Costus comosus

NAME CHANGE NOTES: All separate varieties are proposed to be merged as one species.

FULL SCIENTIFIC NAME: Costus comosus (Jacq.) Roscoe

STATUS : stat. nov.

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:
- Alpinia comosa Jacq. (1791) - Costus comosus (Jacq.) Roscoe var. bakeri (K.Schum.) Maas - Costus bakeri K.Schum. (1904) - Costus quasi-appendiculatus Woodson ex Maas (1972) - Costus maritimus Standl. & L.O.Williams (1951)

BOTANICAL NOTES:
There are several changes proposed to the taxonomy of the species Costus comosus (Jacq.) Roscoe. In his 1972 monograph, Paul Maas combined the species Costus bakeri K. Schum. into Costus comosus, but he established two formal varieties: C. comosus var. comosus and C. comosus var. bakeri, based upon the indument of the upper side of the leaves and bracts. Var. comosus was described as having leaves "densely puberulo-villose" with bracts not "scabrid to the touch". Var. bakeri was described as having leaves "glabrous to sparsely strigose" and bracts "often somewhat scabrid to the touch". Dr. Maas has now proposed to unite those two varieties after finding many intermediates between the two varieties, based on the indumenta. He also has concluded that the species Costus quasi-appendiculatus Woodson ex Maas that was included as a separate species in 1972, should be made a synonym within Costus comosus - thus merging three existing taxa into this one species. He also maintains that the species Costus maritimus Standl. & L. O. Williams should remain as a synonym of Costus comosus.

The type for Costus comosus as established in 1972 was the drawing on Plate 202 from Jacquin's Icon. Pl. Rar., originating from Caracas, Venezuela, which was annotated on the print as Alpinia comosa. Since then, Dr. Maas discovered a specimen in the herbarium at the Natural History Museum in London, England, and this will be designated as the lectotype in place of Jacquin's plate.

Generally speaking, Costus comosus is characterized by its appendaged (or sub-appendaged) bracts and pure yellow tubular flowers. The ligules are truncate and short (1-6 mm long) with leaf petioles 2-10 mm long. The bracts and their appendages are either red, or reddish green (some forms nearly completely green). Maas describes the appendages as being either "horizontally spreading or ascending in the living plants, usually reflexed when dry …", but in all the forms I have seen, the bract appendages are descending in the living plants, except perhaps at the very apex of the inflorescence. The appendages of most forms are acutely triangular in shape, but some of the forms he is including in this species are broader and rounded. The yellow tubular flowers seem to be quite consistent across the many forms of this species.

After visiting all the regions where the various forms occur, except for Venezuela, I have concluded that there are five distinctly different phenotypes included in this species, and that with further research these may well be established (or re-established) as separate species. 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. Samples from four of the five forms listed below were included in the phylogeny. The form from the type locality was not included, but a sample from nearby eastern Colombia will be added later as part of a more complete phylogeny. These forms were well separated into separate highly supported clades. A sample of the widely cultivated form, my accession R3031, was whole genome sequenced in the Chelsea Specht Lab.

As shown from the limited sampling completed so far, the lineages of the Mesoamerican and Central American forms are on a completely separate branch from the South American forms. The former Costus bakeri from Pacific Mexico and Guatemala is shown to be closely related to the Costus maritimus from the steep Pacific bluffs of the Osa Peninsula of Costa Rica. A third clade is represented by samples of the form with a globular shaped inflorescence and bicarinate bracteoles that is found in the mountains of Panama (M9514, R3494, and R3495).

The South American forms are found on a completely separate part of the phylogeny tree, grouped together with the horticultural form (R3031 & 1999-0126011) that is sometimes incorrectly identified as Costus barbatus. Also in this tight group is the new species Costus cochabambae that differs only by the color of the bracts and length of the calyx, and the "La Chonta" plant that is believed to be a natural hybrid with Costus scaber.

The pages with photos and descriptions of these phenotypes may be found at the following links on this website:

I am assuming that the type form from Venezuela is similar to the form I saw at Santa Maria de Boyacá, in the foothills at the base of the eastern slopes of the Andes in Colombia. Detailed photos of my accession from there are on the page for R3308. The form I saw here is distinguishable from the other forms listed above by the shape or the inflorescence with long, acutely triangular bract appendages and the stems are quite thin and tightly spriraling. The plants there are quite consistent with the illustration from Jacquin that was based on a plant near Caracas, Venezuela. This collection has not yet been included in the molecular phylogeny, but will be interesting to see where it shows up on the tree.

I have not seen the living plants from the type locality, but in checking several herbaria specmens from Venezuela, they seem to have a similar inflorescence shape with narrow, acute bract appendages. Based on the specimens in Venezuela, this form flowers in the rainy season as do most Costus species.

HORTICULTURAL NOTES:
Based on information at the Botanic Gardens Conservation International (BGCI) this species is in ex situ cultivation at 28 botanical gardens world wide. Nearly all of these reported accessions are probably in the commonly cultivated horticultural form that is often confused with Costus barbatus. The other forms of C. comosus are not widely cultivated.

ACCESSIONS:Click links (if any) to see details of individual collections. R3308-


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Photos (if available) of Taxon ID 4035
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Costus comosus type specimen - Click to see full sized image
Photo# 473 Accession# R0
Costus comosus type specimen


Costus comosus type specimen - Click to see full sized image
Photo# 474 Accession# R0
Costus comosus type specimen


Costus comosus, horticultural form, photo from Skinner R2947, cultivated plant, origin unknown - Click to see full sized image
Photo# 426 Accession# R2947
Costus comosus, horticultural form, photo from Skinner R2947, cultivated plant, origin unknown


Costus comosus, maritimus form, photo from Skinner R3208, Osa Peninsula, Costa Rica - Click to see full sized image
Photo# 427 Accession# R3208
Costus comosus, maritimus form, photo from Skinner R3208, Osa Peninsula, Costa Rica


Costus comosus, cultivar 'Cherry Drops', photo Skinner R3308, Santa Maria de Boyaca, Colombia. - Click to see full sized image
Photo# 181 Accession# R3308
Costus comosus, cultivar 'Cherry Drops', photo Skinner R3308, Santa Maria de Boyaca, Colombia.


Costus comosus, cultivar 'Cherry Drops', flower details,  photo Skinner R3308, Santa Maria de Boyaca, Colombia. - Click to see full sized image
Photo# 182 Accession# R3308
Costus comosus, cultivar 'Cherry Drops', flower details, photo Skinner R3308, Santa Maria de Boyaca, Colombia.


Costus comosus, Panama bicarinate bracteole form, photo from Skinner R3500, Fortuna area, Panama - Click to see full sized image
Photo# 428 Accession# R3500
Costus comosus, Panama bicarinate bracteole form, photo from Skinner R3500, Fortuna area, Panama


Costus comosus, Panama bicarinate bracteole form, photo from Skinner R3500, Fortuna area, Panama - Click to see full sized image
Photo# 429 Accession# R3500
Costus comosus, Panama bicarinate bracteole form, photo from Skinner R3500, Fortuna area, Panama