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 ofspecialists, just a small fraction ofwhom 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+ max> oH+, ol3C, patterns of 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