HOW MUCH IS KNOWN ABOUT BROMELIACEAE IN 1994?

7 Pages·1994·0.18 MB·

by  Benzing, David H

Selbyana 15: 1-7
HOW MUCH IS KNOWN ABOUT
BROMELIACEAE IN 1994?
DAVID H. BENZING
Department of Biology, Oberlin College,
Oberlin, Ohio 44074 USA
If access and utility alone dictated scientific no exhaustive review of the immense literature
interest, much less would be known about Bro is attempted, only highlights of accomplish
meliaceae today. Fully one half of all its species ments, sprinkled here and there with exhorta
grow in trees, many in remote rain forests. An tions and a bit of guarded speculation. But first
other sizable group of terrestrials similarly dis we need some statistics, current and projected,
courages study by occurring in roadless, bleak, and then some thoughts about the magnitude of
upper montane habitats (e.g., Navia, Puya, many the task and the nature of the goals. Areas of
Tillandsia spp.) especially in South America. inquiry follow, each updated to reflect current
Commercial promise has not provided much en status and lastly, a concluding remark.
couragement for researchers either. Beyond the
pineapple, some widely marketed ornamentals,
SYSTEMATICS, TAXONOMY AND
and a few minor fiber products, bromeliads sim
EVOLUTION
ply offer too little potential to merit funding any
where near that invested to study the more wide Bromeliaceae is the largest, almost exclusively
ly useful Poaceae, Fabaceae, Rosaceae and their American family (one African Pitcairnia sp.) of
kind. Nevertheless, bromeliads have attracted flowering plants. Likewise, its basic tropical char
more than their share of scholarship beginning acter and relative youth are beyond dispute.
with the attentions of an impressive array of However, many additional points, including
nineteenth century, comparative and functional much of its taxonomy, are more equivocal. Ge
morphologists (e.g., Haberlandt, Mez) and plant neric alignments continue to shift and the num
geographers (e.g., A. F. W. Schimper). Brome ber of described species keeps growing, neither
liaceae continues to attract an ever-widening with much likelihood of closure any time soon.
group ofs pecialists, just a small fraction ofw hom Family size has already expanded from the 2110
have authored the contents of this entire volume binomials recognized in Smith and Down's three
of Selbyana. volume monograph (1974, 1977, 1979) to about
Enough information has been compiled on 2700 (Luther, pers. comm.). More additions
Bromeliaceae to warrant a comprehensive, tech should be expected, many contributed by intrep
nical monograph, something not yet available, id amateurs seeking to embellish private collec
but coming soon (Benzing in prep). While noth tions or horticulturists intent on augmenting
ing published in 1994 could even approach a commercial stocks. Three thousand is a reason
complete synthesis, Bromeliaceae is fast emerg able projection for the final tally, but the exact
ing as one of the better known families of flow number of species will depend also on the judg
ering plants. Specifically, perspectives on its or ments of numerous specialists, specifically on how
igin, major radiations, and designs for life under often decisions are made to elevate the status of
an exceptional variety of often stressful growing segregates of the many polymorphic, currently
conditions are expanding rapidly-faster than recognized species (e.g., Tillandsia fasciculata).
progress toward the same goal for most other, Genera will also continue to multiply as so often
comparably large and ecologically diverse clades. occurs as complex groups become better known.
However, knowledge of some aspects (e.g., the For example, Aechmea (currently 10 recognized
nature of the many and often important roles subgenera) and Tillandsia (7 subgenera) will al
these plants play in communities) seems less like most certainly experience this fate. Such move
ly to develop apace due in part to greater im ments are afoot already as are others to combine
pediments to researchers and sometimes simply established genera (e.g., Aechmea and Strepto
because interest continues to be too low. Most calyx, Smith and Spencer 1993). Other author
of the bromeliad literature concerns evolution or ities wisely council patience until changes can be
systematics and this pattern seems likely to con better informed by more comprehensive plant
tinue. collections and deeper analysis (Brown et al.
What follows is a progress report-a briefap 1993). Today, we stand on a threshold. Molec
praisal of where we stand along the route to even ular data, which can more unambiguously re
tual synthesis. Coverage is purposely selective; solve phylogeny than most other kinds, could
2 SELBYANA [Volume 15
easily undermine hasty decisions that will further ing tillandsioids in particular match growing con
clutter the literature and burden users with su ditions (humidity, light and temperature) in
perfluous nomenclature. native habitats.
Inquiry on systematics has not been appor Especially exciting and central to that even
tioned evenly across Bromeliaceae. Most inten tual, evolutionary synthesis is the progress of
sively studied is Tillandsioideae among the three molecular systematists, several of whom work
generally recognized subfamilies, with Pitcair with Bromeliaceae. Ranker et al.'s (1990) anal
nioideae second ahead of Bromelioideae, the ysis of restriction site polymorphisms (cpDNA)
greatest challenge of the three. The compara among species selected to represent all three sub
tively greater structural diversity and presum families heralded what promises to be the first
ably broader genetic variety of the bromelioids of a series of penetrating reports on phylogeny.
is underscored by inclusion of over half of all the They questioned both the reputed basic position
bromeliad genera in this taxon. of Pitcairnioideae within the family and the le
Recent progress toward an evolutionary tax gitimacy of assigning Glomeropitcairnia to Til
onomy ofbromeliads has been assisted by three landsioideae. Coming soon are more complete
developments: (I) a more thorough evaluation reconstructions of relationships based on se
of traditional characters and employment of quence analyses of the gene coding the large sub
newer ones from the same organs (e.g., flowers) unit (rbeL) of rubisco and a second, typically
(2) the emergence of new and more powerful data more variable, and less often used plastid gene
from previously inaccessible sources (e.g., chlo (ndhF) that should allow greater resolution per
roplast genomes) and (3) the application of phe haps to genera (Clark et al. in press, Brown and
netic, and particularly cladistic, analyses that, Randall pers. comm.). We can also expect prog
compared to older methodologies, extract more ress shortly on the question of where Bromeli
biological information from all kinds of valid aceae lies within Liliopsida, specifically its re
data. lationships to suggested sister taxa (e.g.,
Traditional reliance on dried, herbarium ma Rapateaceae, Velloziaceae).
terials has been relieved significantly by the es Cladograms not only display relationships
tablishments .of extensive, documented living among lineages, they can help resolve the origins
collections (e.g., at the Marie Selby Botanical (often multiple in Bromeliaceae) and modifica
Gardens). Supplies of fresh and wet-preserved tion over time of ecologically important plant
materials to examine delicate organs (e.g., stig characteristics such as CAM, epiphytism and the
mas) have been further supplemented by more utilization of anta for dispersal and nutrition (e.g.,
comprehensive field work, aided recently by a Chase and Hills 1992). Gilmartin and Brown
network of on-site collectors (e.g., Gilmartin and (1986) recognized this potential in their attempt
Brown 1986). Fresh material has also provided to determine the status (apomorphic or pleiso
a fairly complete picture of the bromeliad karyo morphic) of xerophytism and mesophytism in
.type and its evolution (Brown and Gilmartin subgenus Phytarrhiza of Tillandsia. Both con
1989). Particularly revealing is Brown and Ter ditions occur in other parts of Tillandsia and
ry's(1992) study of petal scale ontogeny that Vriesea and repeatedly elsewhere in the family.
casts serious doubt on the wisdom of relying so Accurate alignments within Bromeliaceae of ad
heavily on this appendage to distinguish tilland ditional, aberrant genera like Brocchinia will in
siaid and probably some otherbromeliad genera. crease opportunities for similar sorts of deriva
These structures may enhance the delivery of tive analysis, for example, whether the absorptive
nectar, but their apparent, relatively recent evo capacity of the foliar trichome evolved to pro
lution, hence marginal utility to circumscribe at mote mineral nutrition, water balance or both
least some taxa, seems indisputable. phenomena.
Pursuit of additional anatomical details, on
seeds for example, continues (e. g., Gross 1992,
CARBON AND WATER BALANCE
1993). Data on pollen morphology has been ac
cumulating for several decades as well, but so far More data (e.g., H+ oH+, ol3C, patterns of
max>
withou.t the interpretation necessary to inform gas exchange) that indicate the mechanisms of
systematists and other investigators interested in carbon and water balance or reveal their ecolog
pollination syndromes and breeding systems. ical consequences have been collected for the
Trichome structure probably also remains un bromeliads than for species in any other family.
der-utilized for taxonomy and considering the Revelations include the discovery that related
amount of information (e.g., Varadarajan and species with CAM and C3 photosynthesis some
Gilmartin 1987, Benzing .a nd Seemann 1978) times co-occur without substantial differences in
certainly offers much untapped potential to ex water economy (e,g., Griffiths et al. 1986, Grif
plain how the foliar epidermis ofthe dryer-grow- fiths 198.8). Shade tolerance deeper than that pre-
4 SELBYANA [Volume 15
modern techniques have became available to sioideae, the best known of the three subfamilies
plant physiologists. Radiotracers demonstrated by reproductive mechanisms, attracts a variety
substantial uptake of diversF solutes through root of primary pollen vectors including birds, bats,
systems and the foliage of phytotelm forms (e.g, and day- and night-flying insects. Seed dispersal
Nadkarni and Primack 1989). Carnivory is now is more uniform (anemochory), but not consis
well documented in Brocchinia reducta (e.g., tent if air worthiness and tendencies to adhere
Givnish et al. 1984) and probably operates at a to specific tested substrates reflect performances
less specialized level in Catopsis berteroniana. in nature (Bennett 1991) Substantially less in
Owen and Thompson (1988) assessed the fine formation has been reported about Pitcairnioi
structure of the foliar trichome of Brocchinia re deae, but seed size and form indicate consider
ducta and demonstrated how these appendages able variation in mobility, probably more than
probably support carnivory by absorbing the characterizes the tillandsioids. Least known by
products of degraded prey. Tillandsioid tri floral and dispersal biology, except for those myr
chomes need to be compared with those of Broc mecochorous ant-nest flora, is Bromelioideae. As
chinia. Additional study is also required to es berry producers, members of this taxon engage
tablish how the much more common in relationships with fauna beyond those arbo
noncarnivorous phytotelm bromeliads process real ants and dispersal biology is accordingly
litter rather than prey for nutrition. Diverse shoot complex. Fruits appear to be attractive to birds
forms and varied microflora and microfauna in (e.g., odorless white, blue, many Aechmea spp.),
phytotelmata indicate that different symbiotic bats (e. g., drab, smelling of rotten fruit, some
biota and methods of processing mediate nutri Billbergia spp.), and nonvolant mammmais (e.
ent flux for these bromeliads (e.g., Bermudes and g., yellow, orange hidden in foliose infloresences,
Benzing 1991). many Nidularium spp.). Berries of some Ronn
Two forms of myrmecotrophy occur in Bro bergia spp. rupture to eject seeds several meters
meliaceae. Ant-house Tillandsia spp and prob indicating that mechanical enhancements some
ably additional, similarly accommodating taxa times supplement or replace animal carriage.
(e.g., Aechmea bracteata) are fed by ant colonies Information on the breeding systems of bro
residing within inflated leaf bases (Benzing 1991). meliads is scattered and the impacts on the ge
Nutrient budgets and the importance of the ants netic structure, and isolation of populations and
to the plants will require deeper inquiry to es speciation still poorly known. Some populations
tablish. Another group ofbromelioids (e.g., sev routinely fruit autogamously; many more out
eral Aechmea and Streptocalyx spp.) regularly cross through a variety of agencies ranging from
root in ant cartons, sometimes to the near ex dioecism and self-incompatibility to various di
clusion of other substrates (e.g., Davidson 1988). chogamous and herkogamous arrangements
Chemical attractants on seeds assure successful among the self-fertile types. Populations of only
dispersal by foraging ants. However, many other three species, predominantly epiphytic Tilland
aspects of these systems, for example, whether sia ionantha and T. recurvata and terrestrial
plant nutrition reflects reliance of ant-provided Aechmea magdelenae have been comprehen
substrates, remain obscure. Atmospheric bro sively examined (> 20 loci) to determine genetic
meliads continue to be employed to monitor air structures (Soltis et al. I 987, Murawski and
quality (Schrimpff 1981, Benzing et al. 1992) be Hamrick 1990). The latter species relies more
cause of their normal reliance on the atmosphere heavily on ramets to colonize understory habi
and canopy washes for required ions. Extraor tats, possibly because soil, relative to arboreal
dinary capacities to accumulate a variety of ad substrates, tends to be more expansive and per
ditional anthropogenic substances underlies their manent. Bennett (1991) demonstrated propor
utility for pollution survalence; these same qual tionally greater dependence on sexual than asex
ities could prove useful on a broader scale to ual reproduction in epiphytes compared to
measure important variables related to global lithophytes among a group of Tillandsia spp.
change (Lugo and Scatena 1993). chosen to represent both habits.
The bromeliad literature documents how ear
lier interest (e.g., Downs in Smith and Downs
1974) in the physiology of flowering and fruit
REPRODUCTIVE BIOLOGY
development has diminished. Many populations
Reproductive biology, like systematics and respond to photoperiod and very likely cycling
evolution, has attracted more than its share of temperatures and rainfall also cue important life
the scholarly attention devoted to Bromeliaceae. history events. Inquiry on seed physiology has
Numerous reports document modes of pollina moved at about the same slow pace although
tion of specific species (Sazima et al. 1989). Seed previous studies indicated differences in viability
dispersal has received lower priority. Tilland- and dissimilar responses to light and tempera-
1994] BENZING: BROMELIADS 3
vious1y documented for most CAM plants pre (e.g., Vriesea josteriana, Benzing and Friedman
vails in certain other brome1iads (e.g., Aechmea 1981). Additional inquiry on the carbon and wa
magdalenae, Pfitsch and Smith 1988). Manyad ter balance mechanisms of seedlings and adults
ditional CAM species grow better in partial shade of C3 tillandsioids could help test hypotheses
than full sun (e.g., Bromelia humilis ) and may concerning the role of heterochrony and the evo
be relatively poorly suited for the kinds of ter lutionary status of xerophytism in Tillandsioi
restrial environments often associated with CAM. deae (Adams and Ma in 1986). Meanwhile, the
On the other hand, some bromelioids are near controversy over the nature of ancestral envi
record holders for H+ max (474 mol H+ /m-3 for ronments continues (e g., Smith 1989), a subject
Aechmea nudicaulis). likely to defy resolutio until a phylogeny (below
Ananas spp. are providing insights on how plant the genus) is availabl to polarize ecologically
performances under different growing conditions decisive character stat s.
have been altered by indigenous agriculture (Me Whether or not CA represents the most ef
dina et al. 1991). Interactions among Nand ficacious means to fix O everywhere species so
2
moisture supplies and PPFD (photosynthetic equipped occur, drou t limits the productivity
photon flux density) that promote different out of many Bromeliacea and probably more de
comes (e.g., yield, water use efficiency, citric vs. cisively so than scarci ies of any other resource.
malic acid synthesis) under specific conditions The importance of dr ught as a selective force
in CAM plants in the field are probably best is apparent in those b meliads that demonstra
known in Bromeliaceae. Widely noted, but not bly achieve some oft e most favorable transpi
yet resolved to causes and biological conse ration ratios on record (Smith 1989). Some long
quences are the mechanisms responsible for the standing questions ab ut water balance remain
heavy and variable reliance on respired, com only partially resolve , for instance, whether or
pared to atmospheric, CO for nocturnal acidi not water vapor can ignificantly relieve dehy
2
fication that so dramatically characterizes many dration (e.g., Martin nd Schmitt 1989). Low
bromeliads (Smith 1989). (compared to higher) ater vapor pressure def
Longer-term monitoring in the field and fuller icits in surrounding a r allow all land plants to
understanding of the subcellular aspects of CAM conserve moisture, ut claims continue that
are needed to determine if and how this syn shoots of some of the eavily trichomed tilland
drome benefits bromeliads under the many dif sioids hydrate directl from moist air without
ferent environmental conditions prevailing where prior condensation 0 absorptive surfaces. The
these plants grow. What regulatory processes and foliar trichome of Till ndsioideae merits closer
environmental and internal cues determine the scrutiny to see how i aids water balance and
sources, fluxes, and metabolic fates of carbon additionally, to what xtent the variously struc
during CAM? In addition to its capacity to im tured and positioned shield matches humidity
prove water economy, CAM may reduce vul and other conditions i native habitats.
nerability to photodamage or promote N econ
omy under appropriate circumstances. CAM may
MINERAL UTRITION AND
be most important to some bromeliads for ben
efits other than water economy or it could affect
survival only during uncommonly dry years. Fit Occasional reports ontinue to appear on the
ness may not be strongly dependent on the type mineral nutrition of romeliaceae. Several or
of photosynthetic pathway possessed by phyto namentals have prove amenable to hydroponic
telm species native to ever-wet forests and in culture and success 0 conventional media in
stead may reflect conditions in ancestral more dicated no unusual lant requirements (e.g.,
than contemporary habitats. Bromeliaceae do Schmitt 1982). Meth ds have been developed
seem to exceed most other families in the variety for the routine ascepti micropropagation of ad
of plant characters associated with CAM and the ditional taxa, includin some endangered species
kinds of stresses its members encounter on often (e.g., Mercier and Ker auy 1992). Again, widely
demanding substrates. Accordingly, more of the used basal media pro ed effective. Within the
full array of benefits CAM imparts to land flora decade transgenic mat¢rials that combine desir
may be expressed in this family compared to able horticultural qualities will probably reach
most others. the commercial market. Superior shoot form and
Contrary to the CAM types, little attention has desired leaf and infloresence color and texture
been devoted to the C3 bromeliads, for example (historically the highest priorities for hybridizers)
to their light relations. Particularly intriguing are will probably remain the major goals.
the functional correlates of the uneven, but reg Bromeliaceae exceed most families in the va
ular distributions of chlolorophyll and other pig riety of nutritional modes utilized, all of which
ments in the foliage of certain phytotelm species have attracted at least passing attention since
6 SELBYANA [Volume 15
originated. Should those species (e.g., Tillandsia rbeL sequence comparisons. Ann. Missouri Bot.
usneoides, Bromelia humilis) with proven value Gard.80.
DAVIDSON D.W. 1988. Ecological studies ofneotrop
to the study of the widely-occuring aspects of
ical ant gardens. Ecology 69: 1138-1152.
stress physiology continue in that service, in
GENTRY A.H. AND C.H. DoDSON. 1987. Diversity
sights on how this family has so successfully col
and biogeography of neotropical vascular epi
onized the canopy and other demanding sub phytes. Ann. Missouri Gard. 74:205-233.
strates will become clearer. However, input on GILMARTIN A.J. AND G.K. BROWN. 1986. Bromeli
a variety of important, but unique features of aceae: an international cooperative research pro
these plants (e.g., the biology of their foliar tri ject. Taxon 35:107-109.
chomes and the workings of phytotelmata) will ---AND ---. 1986. Cladistic tests ofhypoth
require the attention of investigators specifically eses concerning evolution of xerophytes and mes
interested in these plants. Finally, elucidation of ophytes within Tillandsia subgenus Phytarrhiza
(Bromeliaceae). Amer. J. Bot. 73:387-397.
the many roles Bromeliaceae play in neotropical
GIVNISHT.J., E.L. BURKHARDT, R. HAPPEL AND J. WE
ecosystems as resources for other biota and as
INTRAUB. 1984. Carnivory in the bromeliad
influences on basic ecosystem processes will re Broeehinia reducta with a cost/benefit model for
quire more integrated and multi-disciplinary ap the general restriction of carnivorous plants to
proaches than we have seen so far. sunny, moist nutrient-poor habitats. Amer. Nat
uralist 124:479-497.
GRIFFITHS H. 1988. Carbon balance during CAM: an
assessment of respiratory COl recycling in the epi
LITERATURE CITED phytic bromeliads Aeehmea nudieaulis and Aeeh
mea fendleri. PI. Cell Environm. 11 :603-611.
ADAMS W.W. AND C.E. MARTIN. 1986. Morpholog ---, U. LUTTGE, K.H. STIMMEL, C.E. COOK, N.M.
ical changes accompanying the transition from ju GRIFFITHS AND J.A.C SMITH. 1986. Comparative
veni1e(atmospheric) to adult (tank) forms of the ecophysiology of CAM and C3 bromeliads. III.
Mexican epiphyte Tillandsia deppeana (Bromeli Environmental influences on CO2 assimilation and
aceae). Amer. J. Bot. 73:1204-1214. transpiration. PI. Cell Environm. 9:385-393.
BENNETT B.C. 1991. Comparative biology of Neo GROSS E. 1992. Die Samen der Bromeliaceae. Bro
tropical epiphytic and saxicolous Tillandsia spe melie 1992(3):61-66.
cies: population structure. J. Trop. Ecol. 17:361- ---. 1993. Die Samen der Bromeliaceae (2). Bro
371. melie 1993(1):13-18,25-26.
BENZING D.H. 1981. Bark surfaces and the origin and ---. 1993. Die Samen der Bromeliaceae (3). Bro
maintenance of diversity among angiosperm epi melie 1993(2):53-55.
phytes: an hypothesis. Selbyana 5:248-255. LAESSLE A.M. 1961. A micro-limnological study of
---. 1991. Myrmecotrophy: origins, operation, and Jamaican bromeliads. Ecology 42.:499-517.
importance. In Ant-plant interactions. c.R. Hux LuGO A.E. AND F.N. SCATENA. 1992. Epiphytes and
ley and D.F. Cutler eds, pp 353-373. Oxford climate change research in the Caribbean: a pro
--AND J. SEEMANN. 1978. The foliar epidermis posal. Selbyana 13: 123-130.
in Tillandsioideae (Bromeliaceae) and its role in MARTIN C.E. AND A.K. SCHMITT. 1989. Unusual wa
habitat selection. Amer. J. Bot. 65:359-365. ter relations in the CAM atmospheric epiphyte
--AND W.E. FRIEDMAN. 1981. Patterns offoliar Tillandsia usneoides L. (Bromeliaceae) Bot. Gaz.
pigmentation and their adaptive significance. Sel 150:1-8.
byana 5:224-240. MEDINA E., U. LUTTGE, F. LEAL AND H. ZIEGLER. 1991.
--, J. ARnlTIl, L.P. NYMAN, P.J. TEMPLE AND J.P. Carbon and hydrogen isotype ratios in bromeliads
BENNETT. 1992. Effects of ozone and sulfur diox growing under different light environments in nat
ode on four epiphytic bromeliads. Environm. Exp. ural conditions. Bot. Acta. 104:47-52.
Bot. 32:25-32. MERCIER H. AND G.B. KERBAUY. 1992. In vitro mul
BERMUDES D. AND D.H. BENZING. 1991. Nitrogen tiplication of Vriesea fosteriana. PI. Cell Tissue
fixation in association with Ecuadorean bromeli Organ Cult. 30:247-249.
ads. J. Trop. Ecol. 7:531-538. NADKARNI N.M. 1984. Epiphyte biomass and nutri
BROWN G.K., H.E. LUTHER AND J.W. KREss. 1993. ent capital ofa neotropical elfin forest. Biotropica
Comments on the responsibilities of taxonomists. 16:249-256.
J. Bromeliad Soc. 43:154-157. ---AND R.B. PRIMACK. 1989. The use of gamma
-- AND A.J. GILMARTIN. 1989. Chromosome spectrometry to measure within-plant nutrient al
numbers in Bromeliaceae. Amer. J. Bot. 76:657- locations of a tank bromeliad, Guzmania Ungu
665. lata. Selbyana 11:22-25.
--AND R.G. TERRY. 1992. Petal appendages in OWEN T. AND W.W. THOMPSON. 1988. Sites of leu
Bromeliaceae. Amer. J. Bot. 79:1051-1071. cine, arginine, and glycine accumulation in the
CHASE M.W. AND H.G. HILLS. 1992. Orchid phylog absorptive trichomes of a carnivorous bromeliad.
eny, sexuality, and fragrance seeking. Bioscience J. Ultrastruct. Molect. Struct. Res. 101:215-223.
42:43-49. PAOLETTI M.H., R.A.J. TAYLOR, B.R. STINNER, D.H.
CLARK W.D., B.S. GAUT, M.R. DUVALL AND M.T. STINNER AND D.H. BENZING. 1991. Diversity of
CLEGG. (in press). Phylogenetic relationships of soil fauna in the canopy and forest floor ofa Ven
the Bromeliaceae and related monocots based on ezuelan cloud forest. J. Trop. Ecol. 7:373-384.
1994] BENZING: BROMELIADS 5
tures that probably reflect adaptations to specific through the nutrients they and associated debris
growing conditions sequester, probably deny phorophytes and per
haps other soil-rooted flora adequate nutrition
under certain conditions (Benzing and Seemann
ECOWGY AND IMPACTS IN ECOSYSTEMS
1978). At the same time, these and co-occurring
More is known about the ecology of the epi epiphytes may increase system-wide capacity to
phytic than terrestrial bromeliads. Co-ocurring intercept and store key elements for eventual slow
species in dense forests at a variety of locations release (Nadkarni 1984). Additional benefits ac
segregate within canopies according to exposure crue to forest residents from the humidity created
and humidity more or less as Pittendrigh (1948) by evaporation from phytotelmata. Leafaxils may
described as the pattern in the mountains of contain the only drinking water and provide the
northern Trinidad. Ecophysiologists have iden most durable, moist refuges during long dry sea
tified a number ofu nderlying structural and func sons. No doubt, patterns of aggregate nutrient
tional characters (as described earlier in the sec use and productivity change markedly as forests
tion on carbon and water balance) that dictate become heavily colonized with bromeliads and
plant occurrence at specific locations in the can the additional flora their presence encourages.
opy. While host identity, the size of the sup Contributions to overall forest phytodiversity are
porting axis, and other aspects ofthe substratum apparent in the lists ofa dditional epiphytes, many
(e.g., bare or moss-covered) sometimes influence supported by bromeliads, that constitute up to
distributions secondarily, epiphytic bromeliads 35% of the total flora of some montane forests
are generally less fastidious about anchorages than (Gentry and Dodson 1987).
much other arboreal flora, especially the orchids. Diverse terrestrial, including lithic, substrates
Many populations ofbromeliads with similar if support extensive, additional Bromeliaceae,
not identical cultural requirements grow inter sometimes enough to dominate the associated
spersed, apparently without clear spacing and may floras. Land-based communities with substantial
achieve high local diversities in part in response and greater bromeliad presences occur on the
to appropriately scheduled substrate turnover ground at high elevations (up to 4400 m in the
(Benzing 1981). Phytotelm types furnish rooting Andes), occupy nearly rainless coastal deserts
media for more demanding flora and create high (Peru), and those inland (Hechtia, Dyckia), grow
quality habitat for myriad microflora and fauna, virtually unaccompanied by other vascular veg
both vertebrates and invertebrates, with perva etation on cliff sides, form characteristic assem
sive biological consequences. blages along humid Atlantic coasts (e.g., Brazil
Bromeliads, more than members of other fam ian restingas), and form the understories in certain
ilies, often provide the superstructure for exten humid forests (e.g., Aechmea magdalenae). Some
sive communities, particularly in the canopies of ofthese species also occur as epiphytes and many
humid montane forests occurring between about more possess similar form and function, in effect,
300-3000 m. What so far have been preliminary features that blur the distinction between what
studies only, provide a glimpse of the impact of their obligate relatives suggest are more distinct
this compartment on important processes in sup habits. One of the most interesting of the little
porting ecosystems and early indications suggest researched aspects of bromeliad biology con
substantial significance. Some bromeliads may cerns the determinants of habitat choice, which
achieve keystone status as essential resources in this ecologically varied family must be ex
(mainly housing) for some of the most aggressive traordinarily diverse and sometimes exception
and abundant ants in Neotropical forests (Wilson ally precise.
1987). On a broader scale, the densities and di
versities of invertebrates associated with the hu
CONCLUDING REMARKS
mus contained in leafaxils may exceed those in
adjacent suspended soils and the ground below Research on the evolution, systematics, nat
(e.g., Paoletti et al. 1991). Physical conditions in ural history, structure, and ecophysiology ofBro
bromeliad phytotelmata have not yet received meliaceae is moving forward at a quickening pace.
enough attention (e.g., Laessale 1967) to fully Soon, probably within the next two decades, bro
explain why they support so many and such var meliad phylogeny will be sufficiently understood
ied kinds of residents. Insights on the events to associate populations into natural genera and
within phytotelmata that make them high-qual these taxa in turn into more natural tribes and
ity substitutes for nutritive soil will require the subfamlies. This framework in turn will provide
co-ordinated efforts of microbiologists and spe opportunity to establish where (in which lin
cialists knowledgeable about the workings ofvar eages), how often, and possibly when the char
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