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The Cutting Edge
Volume XIV, Number 3, July 2007
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Season's Pick | Annotate your copy
SEASON'S PICK: Selenicereus inermis (Otto) Britton & Rose
vs. S. wercklei (F. A. C. Weber) Britton & Rose (Cactaceae):
a taxonomic and photographic showdown!
Ever since INBio's survey of the area upriver from the long-planned-to-be-dammed Río
Grande de Térraba gorge [see
The Cutting Edge 7(2):
1, Apr. 2000], we have been nurturing a cutting from the spineless, scandent, and epiphytic
cactus that we reported at that time as being a new in-country disjunct of the endemic
Selenicereus wercklei. From the outset, we were suspicious that this south(eastern)
entity might prove to be something different; its stems are slightly thicker (ca. 2 cm) and with
fewer [3–5(6)] and more prominent ribs than the typical, northern populations of S.
wercklei (with ca. 1 cm, 6–9+-ribbed stems):
Térraba plant/Guanacaste plant
In the Selenicereus key of Britton and Rose (The Cactaceae. Vol. 2.
1920), two spineless spp. were recognized:
- Ribs prominent, 3–5; flowers white.......S. inermis (Venezuela and Colombia)
- Ribs low, 6–12; flowers red...................S. wercklei (Costa Rica)
Could the plant from the Térraba region be S. inermis? Certainly its
rib features suggested this, but we still had not seen flowers. Finally our
plant—having nearly perished but eventually surviving and now thriving—flowered
this past season (seven years flew fast!), and our suspicions that its flowers might differ
from those of the more northern populations were confirmed. But immediately we noticed
something awry, with respect to the Britton and Rose key: if anything, the flower
color was reversed, the outer tepals of the plant with few-ribbed stems being red, vs. green
in the plant with more abundantly, but less prominently ribbed stems!
In the following series of photos, the flower on the left is from the Térraba plant,
the one on the right from a plant cultivated at a house in Tibás (Valle Central), very
near INBio. The Tibás plant, which flowers every year during this season, is of
undetermined wild origin, but is typical of wild plants known from the Cordillera de Guanacaste,
and elsewhere north of San José. The first three photos were obtained by placing
a piece of the Tibas plant, with a mature flower bud, beside a mature bud on the Térraba
plant growing at our house in Santo Domingo, and watching the two open in the evening.
In summary, we list here the most noticeable differences between the flowers of these two plants:
- The Térraba plant has the outer tepals red, vs. green in the Tibás plant
- The Térraba flowers are larger, have a longer tube and tepals, and a thicker tube and
- The outer tepals soon become reflexed in the Térraba plant, but remain erect or patent
in the Tibás plant.
- The stigmas are hidden among the anthers in the Térraba plant, but extend beyond the
anthers in the Tibás plant.
- The Térraba flowers have a sweet, lily-like fragrance that gives way to a pungent
Tagetes-like fragrance by morning, while the Tibás flowers have a pungent,
Tagetes-like fragrance throughout anthesis.
The motivation for the title of our story is that Selenicereus wercklei was recently
placed in synonymy of S. inermis (see Bauer, Cactaceae Syst. Init. 17:
1–63. 2003). While Dr. Bauer's arguments are cogent and his taxonomy is the
logical one to follow, his statement that "The flowers of all these [Costa Rican plants
with various stem morphology] are the same as in typical S. inermis and therefore I
consider S. wercklei to be a synonym of S. inermis" (p. 48, loc. cit.)
suggests that Selenicereus flowers in Costa Rica are all the same*. Based on our
close look at flowers of two of these plants, such is obviously not the case (though Bauer has
seen specimens of other fertile material with 4–6 ribs that we have not). If these
floral differences were found to be consistenly associated with the two different stem forms,
taxonomic recognition, at least at the subspecific level, would seem to be in order.
One final note: the photo below is of the single, still-maturing fruit on our
Térraba plant, produced by dusting stigmas (of several of its flowers) with pollen from
the Tibás plant! N.B.: both of these plants appear to be self-sterile.
* Selenicereus testudo (Karw. ex Zucc.) Buxb., the only other
Selenicereus that has been known from Costa Rica, is now placed in
Strophocactus, and thought not to belong even to the tribe Hylocereeae.
Photos by B. Hammel. Térraba plant vouchered by Hammel & Pérez
24274 (CR, INB, MO), Tibás plant by Hammel & Pérez 24275 (CR,
INB, MO), Guanacaste plant by Hammel 17810A (CR).