This document summarizes research on the evolution and symbiotic relationships within the Cattleya orchid alliance, with an emphasis on Brassavola nodosa. It discusses how the four genera within the alliance (Brassavola, Cattleya, Guarianthe, and Rhyncholaelia) have diverged in their pollination strategies and relationships with pollinators, despite similarities in their epiphytic lifestyle and wind-dispersed seeds. While Brassavola and Rhyncholaelia are pollinated by moths and produce nectar in a mutualism, Cattleya and Guarianthe rely on deceptive pollination by bees without providing n

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Mariah Harrod
Professor Nydam
Biology 110
16 May 2015
Evolution and Symbioses within the Cattleya Alliance, with Emphasis on Brassavola nodosa
Orchidaceae is so extensively diverse that a count of 25,000 species has been estimated to
represent the vast speciation of the largest flowering plant family (Dressler 2005). As with any
taxonomy, orchids can be categorized along various morphological and genetic characteristics to
reveal evolutionary connections and to provide comparison for how speciation has occurred
amongst similar taxa. The Cattleya alliance—one of eight alliances within the subtribe of
Laeliinae, tribe Epidendreae, subfamily Epidendroideae, family Orchidaceae—includes the
genera Brassavola, Cattleya, Guarianthe, and Rhyncholaelia (van den Berg et al. 2009). All are
neotropical orchids with diminutive seeds well-adapted for epiphytic commensalism, but
Brassavola and Rhyncholaelia are pollinated by moths while Cattleya and Guarianthe are food-
deceptive and rely on bee pollination. However, plastid and nuclear sequencing contradicts that
this similarity constitutes closer evolutionary relationships between Brassavola and
Rhyncholaelia and bee-pollinated Guarianthe and Cattleya (Damon and Salas-Rosblero 2007).
Dispersal of seeds into new suitable microhabitats is critical to the survival of many
plants. To fulfill this necessity, Orchidaceae members have evolved to produce a large quantity
of miniscule, non-plumed seeds (Murren and Ellison 1998). In the 1998 study by Murren and
Ellison, the seeds of the orchid Brassavola nodosa were proven to be highly adapted to

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horizontal, long-distance wind dispersal. The light weight of these embryos allow them to be
transported across large expanses, which ultimately increases likelihood of germination in a
resource-limited environment in which selective pressures are strong (Murren and Ellison 1998).
Further, around 70% of all orchids are epiphytes—meaning they colonize other plants, usually
trees—and accordingly Orchidaceae represents more epiphytic diversity than any other vascular
seed plant family (Gentry and Dodson 1987). This adaptation to produce extremely light seeds is
essentially crucial if survival is linked so closely to the height at which the seed lands. We may
hypothesize that the successful epiphytism of orchids—including other members of the Cattleya
alliance—could have resulted from the initial adaptation for easily wind-borne seeds.
Guarianthe, for example, has been observed as an epiphyte on coffee trees (Damon and Salas-
Roblero 2007). Brassavola has been observed colonizing calabash trees and red mangroves
(Yeaton and Gladstone 1982; Murren and Ellison 1996). Rhyncholaelia digbyana is also an
epiphyte which follows the same pattern of size rather than species preference for plant hosts as
B. nodosa (Zimmerman and Olmsted 1992). Genus Cattleya, too, includes epiphytic species such
as forbesii which have been naturally selected to anchor onto plants for the fitness advantage it
entails (Stancato et al. 2002). This epiphytic relationship is one of commensalism, in which the
orchid benefits immensely from the extra sunlight access and the tree experiences no significant
fitness advantage or disadvantage as a result of the colonization. Indeed, Murren and Ellison
(1996) found that increased exposure to light (as would occur nearer to solar energy at the tops
of tall trees) results in a greater quantity of inflorescences being produced, which then
contributes to the reproductive success of the orchid studied, Brassavola nodosa. The
reproductive success of nodosa, as well as with its closer orchid relatives, is also inextricably

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bound up with the presence of animal pollinators who have helped shape the evolution of the
flowers in mutualisms and parasitic deceptions.
Brassavola nodosa, like many other orchids who rely on animals to pollinate their
flowers, has co-evolved alongside its pollinator through mutualism. This mutualism is
characterized by the orchid providing the carbon compound nectar for the mobile fluid feeder,
whose close proximity entangles it with pollen which is subsequently transported and sometimes
dropped in the ideal location—the pistil of a reproductively suitable receiving flower. Because
pollination and reproduction by orchids is rare (thus the natural selection for orchids having a
large seed set on the occasion that reproduction does occur), observation of the actual pollinia
removal and pollinator-plant interaction is uncommon (Damon and Salas-Roblero 2007).
However, Brassavola has been observed being pollinated by moths and exhibits the
characteristics associated with nocturnal pollination—nightly perfuming, elongated tubes with
deeply buried nectar for long tongues, no color guides for nectar, and hanging white
inflorescences distinctly visible in darkness (Williams 1981). Of the three other genera besides
Brassavola which compose the Cattleya alliance, only Rhyncholaelia has also been observed to
be largely night-pollinated (Damon and Valle-Mora 2008). Like Brassavola nodosa,
Rhyncholaelia glauca is pollinated by the sphinghid moth and has accordingly adapted to
nocturnal attraction methods (Damon and Valle-Mora 2008). R. glauca was actually considered a
member of Brassavola until 1918; this decision was later reinforced when further research used
morphological distinction to divide the two genera by pollinia quantity (Williams 1981).
Accordingly, we observe what appears to be a close evolutionary history between these two
genera and especially between the moth-pollinated species B. nodosa and R. glauca, both of

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which engage in mutualisms with their pollinators by producing nectar which only the long
tongues of moths and butterflies may reach before spreading the orchid pollen.
On the other hand, relative Guarianthe is largely pollinated by daytime insects such as
the male Euglossine bee (Damon and Salas-Roblero 2007). This specific bee actually pollinates
many different species of orchids at various seasons throughout the year, and thus has
contributed greatly to the reproduction and adaptive radiation of orchids (Damon and Salas-
Roblero 2007). Similarly, Cattleya species such as elongata and tenuis have been observed being
pollinated by queen Bombus (bumblebees) (Smidt et al. 2006). This is significant because non-
rewarding flowers are more likely to attract bee pollinators than moths, and this indicates that
these interactions are deceptive and non-mutualistic and have allowed Guarianthe and Cattleya
to diverge substantially from the moth-pollinated, nectar-producing genera Brassavola and
Rhyncholaelia (Damon and Valle-Mora 2008). In observation, neither of the aforementioned
bumblebee-pollinated species of diverse genus Cattleya actually produces nectar for the bee
which transports the pollen (Smidt et al. 2006). Likewise Euglossine-pollinated Guarianthe
skinneri is also a food deceptive orchid which abstains from using the energy needed to produce
nectar for its pollinator while its scent continues to attract it—thus the orchid benefits while the
bee’s fitness is reduced when unsuccessfully foraging for food (Permberton 2007). In this
manner, Guarianthe and Cattleya seem to have parted ways with Brassavola and Rhyncholaelia
collectively on the basis of nectar production and parasitic deception due to pollinators.
However, if we evaluate the phylogenetic tree based on plastid and nuclear sequencing provided
below, it appears that Rhyncholaelia is actually a closer relative to Guarianthe than to
Brassavola, and Brassavola seems to be more closely related to Cattleya than to Rhyncholaelia.

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van den Berg, C., W.E. Higgins, R.L. Dressler, W.M. Whitten, M.A. Soto-Arenas, and M.W. Chase. 2009. A phylogenetic
study of Laeliinae (Orchidaceae) based on combined nuclear and plastid DNA sequences. Annals of Botany 104: 422.
The phylogenetic tree above uses genetic information from the cells of various orchid
species to compare the similarities between sequences of organisms, revealing the closeness of
their evolutionary relationships. This tree indicates that Guarianthe is the sister genus to
Rhyncholaelia, and that Brassavola only later diverged alongside Cattleya. This seems contrary

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to the morphological and ecological similarities observed by the two moth-pollinated genera in
comparison to the deceptions exhibited by Guarianthe and Cattleya. Perhaps further research on
the remainder of the species within all four of these genera would provide some insight on
whether the evolution of food deception occurred once and was inherited or evolved several
times throughout the history of this clade. In the creation of this tree, van den Berg (2009) admits
that relationships among Brassavola, Cattleya, Guarianthe, Rhyncholaelia remain ambiguous
and accordingly further research on their adapted pollination techniques may shed some light on
how this alliance has been honed by mutation, natural selection, and sexual selection over time.
The Cattleya alliance comprises orchids which have evolved with the remainder of their
family to produce a large set of easily wind-dispersed seeds highly rewarding in the rare instance
that reproduction occurs. This production of lightweight seeds has perhaps encouraged the
widespread epiphytism observed in the orchid family (Gentry and Dodson 1987). Tropical
epiphytic orchids, such as those in the Cattleya alliance, often inhabit niches with limited
resources and accordingly prioritize biomass production over reproductive strategies (Damon
and Salas-Roblero 2007). What links these orchids is their low energy use in reproduction.
However, pollination techniques help distinguish members of the Cattleya alliance. While
Rhyncholaelia and Brassavola are moth-pollinated, Guarianthe and Cattleya have been observed
with bee pollinators prone to the fragrant deception of these genera. Accordingly pollination
differences have, along with epiphytism, led to extremely high diversity and speciation amongst
orchids (Dodson 2003). However, the van den Berg (2009) phylogeny using genetic sequencing
indicates a different evolutionary tale in which Rhyncholaelia and Brassavola are not as closely
related as we would anticipate given their similar pollination and the previous grouping of the
former within the prior established genus of the latter.

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Literature Cited
Calvo, R.N. 1990. Inflorescence size and fruit distribution among individuals in three orchid
species. American Journal of Botany 77: 1378-1381.
Damon, A., and P. Salas-Roblero. 2007. A survey of pollination in remnant orchid populations
in Soconusco, Chiapas, Mexico. Tropical Ecology 48: 1-14.
Damon, A., and J. Valle-Morra. 2008. Retrospective spatial analysis of the pollination of two
miniature epiphytic orchids with different pollination strategies in a coffee plantation in
Soconusco, Chiapas, Mexico. Botanical Journal of the Linnean Society 158: 448-459.
Dodson, C.H. 2003. Why are there so many orchid species? Lankesteriana 7: 99-103.
Dressler, R.L. 2005. How many orchid species? Selbyana 26: 155-158.
Freeman, S., K. Quillin, and L. Allison. 2014. Biological Science 2. p. 1133. Pearson, Harlow,
UK.
Gentry, A.H., and C.H. Dodson. 1987. Diversity and biogeography of neotropical vascular
epiphytes. Annals of the Missouri Botanical Garden 74: 205-233.
Jones, H.G. 1973. Synopsis of middle American Brassavola. American Midland Naturalist 89:
499-503.
Murren, C.J., and A.M. Ellison. 1996. Effects of habitat, plant size, and floral display on male
and female reproductive success of the neotropical orchid Brassavola nodosa. Biotropica
28: 30-41.
Murren, C.J., and A.M. Ellison. 1998. Seed dispersal characteristics of Brassavola Nodosa
(Orchidaceae). American Journal of Botany 85: 675-680.
Noguera-Savelli, E., and D. Jáuregui. 2011. Comparative leaf anatomy and phylogenetic
relationships of 11 species of Laeliinae with emphasis on Brassavola (Orchidaceae).
Revista de Biologia Tropical 59: 1047-1059.
Pemberton, R.W. 2007. Pollination of Guarianthe skinneri, an ornamental food deception
orchid in southern Florida, by the naturalized orchid bee Euglossa viridissima.
Lankesteriana7: 461-468.
Schemske, D.W. 1980. Evolution of floral display in the orchid Brassavola nodosa. Evolution
34: 489-493.
Smidt, E.C., V. Silva-Pereira, and E.L. Borba. 2006. Reproductive biology of two Cattleya
(Orchidaceae) species endemic to north-eastern Brazil. Plant Species Biology 21: 85-91.
Stancato, G.C., P. Mazzafera, and M.S. Buckeridge. 2002. Effects of light stress on the growth
of the epiphytic orchid Cattleya forbesii Lindl. X Laelia tenebrosa Rolfe. Brazilian
Journal of Botany 25: 229-235.

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van den Berg, C., W.E. Higgins, R.L. Dressler, W.M. Whitten, M.A. Soto-Arenas, and M.W.
Chase. 2009. A phylogenetic study of Laeliinae (Orchidaceae) based on combined
nuclear and plastid DNA sequences. Annals of Botany 104: 417–430.
Williams, N.H. 1981. Floral fragrance component of Brassavola (Orchidaceae: Laeliinae).
Selbyana 5: 279-285.
Yeaton, R.I., and D.E. Gladstone. 1982. The pattern of colonization of epiphytes on calabash
trees (Crescentia alata HBK.) in Guanacaste Province, Costa Rica. Biotropica 14: 137-
140.
Zimmerman, J.K., and I.C. Olmsted. 1992. Host tree utilization by vascular epiphytes in a
seasonally inundated forest (Tintal) in Mexico. Biotropica 24: 402-407.