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Department of Integrative Biology and Jepson Herbarium, University of California, Berkeley, California 94720
Received for publication March 10, 1998. Accepted for publication September 10, 1998.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Key Words: boojum • Fouquieria • Fouquieriaceae • ITS • long-branch attraction • ocotillo • rooting
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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; Henrickson, 1969a
, 1972
). Relationships within the family have been examined most thoroughly by Henrickson (1972)
using morphological, cytological, and ecological data. From this work, Henrickson proposed the recognition of one genus, Fouquieria (including Idria), three subgenera (Fouquieria, Bronnia, and Idria), and 11 species in Fouquieriaceae (see Table 1). We generated phylogenetic hypotheses for Fouquieriaceae based on molecular data from the 18S–26S rDNA internal transcribed spacer (ITS) region. These trees were used to evaluate the current taxonomy of the group, as proposed by Henrickson and to examine hypotheses of character evolution.
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subgenera of Fouquieriaceae roughly correspond to growth forms. Subgenus Idria and subg. Bronnia comprise the succulent taxa; subg. Fouquieria contains the woody taxa. The succulent species achieve their growth form by an increase in parenchymatous water storage tissue within the secondary xylem and, in F. columnaris, the pith (Humphrey, 1935
; Henrickson, 1969c
). Subgenus Idria contains F. columnaris (boojum tree), a columnar plant with a succulent trunk reaching a height of up to 40 feet (Humphrey, 1935
). Subgenus Bronnia contains F. fasciculata and F. purpusii, both of which have basally succulent trunks. Subgenus Fouquieria contains eight woody (or dendroid) species, split into sect. Fouquieria and sect. Ocotilla. The six species of sect. Fouquieria bear distinct trunks and branching stems. The two species of sect. Ocotilla have a reduced trunk and vertical unbranched stems. In his comparative anatomical study of F. columnaris and F. splendens, Humphrey (1935)
suggested that members of Fouquieriaceae cannot be readily classified as shrubs or as stem-succulents, the two predominant types of xerophytic plants he recognized within the southwestern North American deserts. The shrub forms of subg. Fouquieria possess a degree of cortical succulence, and the succulent forms are not succulent throughout, even in F. columnaris, which possesses nonsucculent branches. Growth forms in the family are intermediate between typical xeromorphic types.
The base chromosome number in Fouquieriaceae is x = 12 (Henrickson, 1972
). Both Fouquieria columnaris and F. burragei are hexaploids (n = 36), F. diguetii is a tetraploid (n = 24), and the remaining species are diploid (n = 12) (chromosome counts for F. formosa are lacking). Henrickson (1972)
suggested that F. burragei is part of a polyploid series including F. macdougalii and the tetraploid F. diguetii. He suggested that F. diguetii may have descended from "F. macdougalii stock" and that F. burragei may have been of amphiploid origin with possible parents including F. diguetii and "some presumably now extinct diploid species having numerous stamens, possibly short, white corollas and spicate or racemose inflorescences" (Henrickson, 1972
, p. 499). Similarly, a species from the F. purpusii and F. fasciculata lineage (subg. Bronnia) may have served as a parent in an amphiploid derivation of F. columnaris (subg. Idria) (Henrickson, 1972
).
With regard to floral characteristics, just over half of Fouquieriaceae species possess stereotypical hummingbird-pollinated flowers, with tubular red corollas containing nectar at the base. All red-flowered species are in subg. Fouquieria. Also in subg. Fouquieria are F. burragei and F. shrevei, both of which have corollas that are pink in bud and white to pink at maturity (Henrickson, 1972
). Members of subg. Bronnia and subg. Idria have corollas that are cream yellow to white throughout their development (Henrickson, 1972
). Members of these two subgenera, as well as F. shrevei, lack floral anthocyanins (Scogin, 1977
). In addition to floral pigmentation, flowers of Fouquieria taxa differ in the number of stamens, the degree of corolla limb reflexion, and their pattern of arrangement in inflorescences.
Fouquieriaceae has been considered closely related to various families and orders since its establishment by De Candolle in 1828
. De Candolle suggested an affinity with Portulacaceae, as did Humboldt, Bonpland, and Kunth
when they first described the genus Fouquieria in 1823 (for expanded discussion and references see Henrickson [1967
, 1972
]). The hypothesized affinity of Fouquieriaceae with Portulacaceae is untenable because Caryophyllales is diagnosed by numerous characteristics (Mabry, 1977
) lacking in Fouquieriaceae. The type specimen for Fouquieria was originally placed in Cantua (Polemoniaceae) by Roemer and Schultes (1819)
. An affinity with Polemoniaceae was also suggested by Nash (1903)
, in the first treatment of Fouquieriaceae, and by Henrickson (1967
, based on pollen comparisons), the author of the most recent treatment. Additional suggestions for the position of Fouquieriaceae have included alignment with Tamaricales (e.g., Hutchinson, 1926
; Takhtajan, 1969
), Violales (e.g., Cronquist, 1981
), Ebenales (e.g., Bessey, 1915
; Morton et al., 1996
), Solanales (e.g., Thorne, 1969
; Scogin, 1977
; both included Polemoniaceae within Solanales), and Ericales (e.g., Dahlgren, Jensen, and Nielsen, 1976
; Jensen and Nielson, 1982
; Hufford, 1992
; Olmstead et al., 1993
). The Ericales clade in which Fouquieriaceae has been placed in molecular trees is broadly circumscribed, including Ebenales taxa among others (Olmstead et al., 1993
). Anderberg (1992)
placed Fouquieriaceae at the base of Asteridae but noted that the family could shift closer to the Ericales clade with increased taxon sampling. The general pattern that has emerged from various phylogenetic analyses is placement of Fouquieriaceae at the base of Asteridae, perhaps within a broadly circumscribed ericalean grouping.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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, and purified on CsCl2 gradients. Two chloroform/isoamyl alcohol extractions and two ethanol precipitations (following isopropanol precipitation) were added to Doyle and Doyle's method. Leaf material was dried and stored in silica gel desiccant prior to DNA isolation. Most DNAs from Fouquieriaceae taxa were generously provided by Sarah Vetault (University of Arizona) and Michael Donoghue (Harvard University), with subsequent collections obtained to provide additional representation within each species, when possible. Outgroup taxa were chosen to represent the various orders with which Fouquieriaceae have been aligned. One ingroup sequence was provided by J. Mark Porter (Rancho Santa Ana Botanic Garden), and a total of nine outgroup sequences were provided by J. Mark Porter, Staci Markos (U. C. Berkeley), and Lena Hileman (Harvard University), as noted in Table 2.
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. For some taxa, double-stranded DNAs were generated using a GeneAmp 9600 with the following conditions: initial denaturation (97°C, 1 min), followed by 40 cycles of denaturation (97°C, 10 s), annealing (48°C, 30 s), and extension (72°C, 20 s increasing 4 s with each cycle), and concluding with a final extension (72°C, 7 min). The polymerase chain reactions (PCR) contained the following components: 5.0 µL 10X PCR buffer II (Perkin Elmer, Foster City, California), 2.5 mmol/L MgCl2, 1.0 mmol/L dNTPs, 2.5 µL glycerol, 0.5 µmol/L ITS-I primer (5’-GTCCACTGAACCTTATCATTTAG-3’; designed by L. E. Urbatsch, Louisiana State University), 0.5 µmol/L ITS4 primer (White et al., 1990
), 1.0 unit AmpliTaq DNA polymerase (Perkin Elmer, Foster City, California), and 1–10 ng DNA, to a total volume of 50 µL. PCR products were cleaned using either Ultrafree-MC 100000 NMWL polysulfone membrane filter units (Millipore Corporation, Bedford, Massachusetts), or Wizard PCR Preps DNA Purification System (Promega, Madison, Wisconsin), following manufacturer's instructions. Sequencing reactions were performed with an Applied Biosystems, Inc. (ABI) PRISM Dye Terminator Cycle Sequencing Ready Reaction Kit (Foster City, California). Sequencing products were cleaned with Centri-sep spin columns (Princeton Separations, Adelphia, New Jersey), and electrophoresed on 4% polyacrylamide gels using an ABI 377 automated sequencer. Sequences were visualized using ABI Sequence Navigator software.
Alignment of ITS 1 and ITS 2 sequences was conducted separately. Sequences from the 5.8S region were not included. Visual alignment of sequences within Fouquieriaceae was achieved readily. Sequence alignment with the outgroups was attempted using Clustal V (Higgins, 1994
) with fixed and floating gap penalties of ten. Sequence divergence between Fouquieriaceae and potential outgroups was substantial, ranging from 33.8 to 50.8%, as was divergence between potential outgroups. Because of these high divergences and alignment difficulties, the full data set was not used. Instead, a data file was created retaining all sequence information within Fouquieriaceae but with all ambiguously aligned regions within the outgroup sequences coded as missing data ("?"). This is similar to the approach taken by Bruns et al. (1992)
to enable retention of sequence information for those sequences with unambiguous alignments in otherwise problematic regions.
Phylogenetic analyses were carried out using PAUP version 3.1 (Swofford, 1993
) and test versions d55-d59 of PAUP* 4.0 (with permission, D. L. Swofford, Smithsonian Institution, personal communication). Multiple analyses were undertaken, both with and without inclusion of outgroup taxa.
Analysis 1 of Fouquieriaceae taxa (without outgroup sequences) employed a branch-and-bound search with the parsimony criterion to find all minimum-length (unrooted) trees. Clade support was assessed with both bootstrap and decay analyses. The bootstrap employed 100 replicates with branch-and-bound searches. Decay analysis employed a branch-and-bound search saving all trees up to six steps longer than the most parsimonious tree. The trees were filtered for progressively shorter tree lengths and a strict consensus tree was calculated at each tree length.
Analysis 2 included all taxa but with partial sequence data, the ambiguously aligned regions in outgroup sequences being coded as missing data. Complete heuristic searches were conducted with 100 replicates of random taxon addition, TBR branch swapping, and MULPARS in effect to find all minimum-length trees and to obtain an outgroup rooting of Fouquieriaceae. Clade support was assessed using the "fast heuristic" bootstrap algorithm available in PAUP*. This algorithm employs less thorough searches than the standard bootstrap algorithm, but provides a conservative estimate of bootstrap values (M. J. Sanderson, U. C. Davis, personal communication).
Analysis 3 employed maximum-likelihood (ML) analysis of ingroup taxa under the HKY85 model of sequence evolution, both with and without enforcement of a molecular clock to determine whether similar topologies would be obtained (consistent with rate constancy of ITS evolution) and to compare with results of the parsimony analyses. The 12 trees from analysis 1 were used as the starting trees for a heuristic search with TBR branch swapping. Base frequencies were empirically assessed. The proportion of invariant sites was left at the default setting of zero. Transition: transversion (K) parameters and shape (
) parameters were estimated on tree number 1 from analysis 1 (6.390220 and 0.193432, respectively), with rate heterogeneity across sites following a gamma distribution with five rate categories.
Analysis 4 was conducted with ingroup taxa using a parsimony criterion, but with various weighting schemes, in consideration of the high transition: transversion (K) ratio estimated on tree number 1 from analysis 1. Heuristic searches with 20 replicates of random taxon addition, TBR branch swapping, and MULPARS in effect were conducted. The transversion:transition weighting schemes employed were 18:10, 2:1, 25:10, 27:10, and 3:1. A weighting scheme of 
18:10 is recommended by Albert and Mishler (1992)
for an estimated transition:transversion (K) ratio of 6.4 and lambda value of 0.1.
Analysis 5 determined the likelihood values both with and without enforcement of a molecular clock for one of two trees generated with a branch-and-bound search of ingroup taxa under the parsimony criterion where the root placement within the ingroup was forced to fall at each of all possible branches. Fewer ingroup sequences were included in this analysis in order to minimize the number of necessary calculations [FC(1), FFA(1), FP(1), FL(1), FO(1), FM(1), FD(1), FB(1), FB(2), FS(2), FSH(1), FF; see Table 3 for abbreviations]. Maximum-likelihood estimates of the transition:transversion (K) ratio (5.756055) and the shape parameter (0.147754) were generated from the same unrooted topology, with rate heterogeneity following a gamma distribution with five rate categories. Base frequencies were empirically assessed. Evolutionary rate heterogeneity across lineages was assessed using a global likelihood-ratio (LR) test (Felsenstein, 1988
; Huelsenbeck and Rannala, 1997
).
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; see Fig. 4 for a phylogram). One hundred data sets for each of 20 possible root placements within Fouquieriaceae were simulated using the Siminator program provided by J. P. Huelsenbeck (University of Rochester). The ingroup topology of input trees was equivalent to that of tree number 1 in the parsimony analysis of only ingroup taxa (analysis 1). Nucleotide frequencies and size of each simulated data set were kept identical to those found in the data set from analysis 2. Transition:transversion (K) ratios, shape parameters, and branch lengths were estimated in PAUP* using a maximum-likelihood criterion for each of the input trees on which the simulated data sets were modeled. Heuristic searches of all simulated data sets were conducted with simple addition of sequences and tree-bisection-reconnection (TBR) branch swapping under a parsimony criterion. Root placements within Fouquieriaceae in the resulting trees were tallied by filtering trees with backbone constraints corresponding to each of 20 possible root placements.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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In analysis 4, three of the five transversion:transition weighting schemes employed resulted in the same 12 tree topologies. The strict consensus of these 12 trees (length 1040 for 25:10 weighting, length 1064 for 27:10 weighting, and length 110 for 3:1 weighting; all are length 86 under unweighted parsimony) is equivalent to the strict consensus of the 54 ML trees from analysis 3 (Fig. 3), except that the weighted-parsimony tree contains less resolution in the Fouquieria formosa, F. leonilae, and F. ochoterenae clade, with the three taxa forming a trichotomy. The search with a 2:1 weighting scheme resulted in 24 trees of length 98, the strict consensus of which lacked resolution within subg. Fouquieria beyond intraspecific groupings and the placement of F. burragei (1) with F. diguetii sequences. Twelve of these 24 trees (length 85 under unweighted parsimony) are compatible with the strict consensus of trees from the unweighted parsimony analysis (Fig. 1), six (length 86 under unweighted parsimony) are compatible with the strict consensus of the ML trees (Fig. 3), and the remaining six (length 86 under unweighted parsimony) are compatible with the strict consensus of the ML trees except that the positions of Fouquieria formosa and F. ochoterenae are reversed. The search with an 18:10 weighting scheme resulted in 12 trees of length 954 (length 85 under unweighted parsimony), the strict consensus of which is equivalent to that of trees from the unweighted parsimony search (Fig. 1).
Analysis 5 results (Table 3) indicate that clock-like evolution can be rejected for all root placements within Fouquieriaceae except (1) between the succulent and woody taxa (equivalent to the midpoint rooting and to the rooting seen in Fig. 4), (2) between subg. Idria and the remaining taxa (equivalent to the outgroup rooting seen in Fig. 2), or (3) between subg. Bronnia and the remaining taxa (Table 3).
Analysis 6 suggests that neither the branch between subg. Idria and remaining taxa, nor between subg. Bronnia and remaining taxa is sufficiently long to act as a long-branch attractor. Of the 31 604 trees generated by analysis of 2000 simulated data sets (100 for each of 20 possible root placements), only in 5% was the root placed between subg. Idria and the remaining taxa, and in only 6% between subg. Bronnia and the remaining taxa (Table 4). The root was placed between the succulent and woody taxa in 15% of the trees, indicating that the branch separating the two groups may indeed act as a long-branch attractor.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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are supported as monophyletic groups based on the ITS data, irrespective of tree reconstruction criterion (parsimony or ML) or rooting method (outgroup, midpoint, or clock-consistent approaches). Within subg. Fouquieria, neither sect. Fouquieria nor sect. Ocotilla are well-supported monophyletic groups in the molecular trees. Those taxa corresponding to sect. Fouquieria are nested within those that correspond to sect. Ocotilla in the ML trees (Figs. 3–4). The reverse is the case in the maximum parsimony topologies (Fig. 1).
Uncertainty in placement of the root in Fouquieriaceae dictates that if the genus Idria, containing I. (Fouquieria) columnaris, is recognized (e.g., Wiggins, 1980
) then the genus Bronnia should also be reinstated for F. purpusii and F. fasciculata to ensure monophyly of Fouquieria sensu stricto (s.s.). The issue of whether to recognize one or three genera in Fouquieriaceae is, however, purely a subjective question of rank (subgenus vs. genus) (see Cantino, Olmstead, and Wagstaff, 1997
).
In his 1972 treatment of Fouquieriaceae, Henrickson presented a "putatively phylogenetic system of relationship" in which he identified four main groups of taxa, corresponding to the subgenera and sections in his taxonomic scheme (Table 1). The four groups Henrickson identified were based on cytological data, anatomical data, and a phenetic analysis of 71 ecological, vegetative, and reproductive characters. He identified Fouquieria leonilae and F. ochoterenae as most representative of ancestral conditions within the family, citing in particular the following characters as primitive: "diploid, ...dorsi-ventral leaves, initial single traces to each sepal, ten stamens, ...6(-12) ovules per ovary." Other species within the family possess dorsiventral or isolateral leaves, a higher but variable number of sepal traces, ten or more stamens, and a higher but variable number of ovules. Henrickson's proposition that Fouquieria leonilae and F. ochoterenae possess the greatest number of plesiomorphic characteristics within the family (1972) is most consistent with the parsimony trees (Fig. 1), assuming that out of the three most reasonable root placements, the root is placed along the branch between subg. Fouquieria and the remaining taxa. From the lineage represented by F. leonilae and F. ochoterenae, Henrickson suggested the derivation of three additional lineages: (1) F. formosa, (2) the putatively polyploid series of F. macdougalii, F. diguetii, and F. burragei, and (3) the ocotillos, F. splendens and F. shrevei. Fouquieria leonilae and F. ochoterenae, together with F. formosa and the polyploid series, constitute the dendroid subg. Fouquieria sect. Fouquieria. Fouquieria splendens and F. shrevei form subg. Fouquieria sect. Ocotilla. The remaining two groups Henrickson recognized are the succulent subg. Idria (F. columnaris) and subg. Bronnia (F. fasciculata and F. purpusii).
The four groups Henrickson identified (1972)
are not, he noted, of equal phenetic distinctiveness relative to each other. The two succulent subgenera are more distinct phenetically from each other and from the woody taxa than are the two woody sections from each other. This impression is supported by the clock-like molecular trees in which the three subgenera are on long branches relative to branches within the subgenera (Fig. 4). Henrickson pointed out that the succulent subg. Bronnia is phenetically intermediate between subg. Idria and woody subg. Fouquieria. His dendrograms indicate a closer phenetic similarity of subg. Bronnia with subg. Fouquieria using ecological and vegetative characters, and a closer similarity with subg. Idria using reproductive characters. Within subg. Fouquieria, Henrickson noted that F. burragei is intermediate between sect. Ocotilla and sect. Fouquieria. This is perhaps a reflection of the hypothesized parental contribution to F. burragei from both sections within subg. Fouquieria, a hypothesis supported by our molecular data.
Outgroups and rooting
Rooting Fouquieriaceae using the outgroup method was problematic due to the levels of sequence divergence between Fouquieriaceae and its potential outgroups. Outgroup sampling in this study was not aimed at determining the placement of Fouquieriaceae relative to other angiosperm families, but was guided by other higher level phylogenetic analyses which included Fouquieriaceae (Anderberg, 1992
; Hufford, 1992
; Olmstead et al., 1993
). Results of analyses including only those portions of the outgroup sequences that were alignable suggest that an ericalean grouping is sister to Fouquieriaceae. This clade, however, has weak support. This result is in agreement with interpretations of a position of Fouquieriaceae close to Ericales (e.g., Anderberg, 1992; Olmstead et al., 1993). The tree shown (Fig. 2) was rooted using Tamarix based on recent evidence that Tamaricaceae falls close to Caryophyllales, well outside of Asteridae sensu lato (Lledó et al., 1998).
Using only the alignable portions of the outgroup sequences placed the root in Fouquieriaceae between Fouquieria subg. Idria (F. columnaris) and the remaining species (Fig. 2). A midpoint rooting results in a basal dichotomy between subg. Fouquieria and both subg. Idria and subg. Bronnia (equivalent to the root seen in Fig. 4). Both of these root placements as well as a root placement along the subg. Bronnia branch are consistent with clock-like evolution of ITS sequences (Table 3). Results from data sets simulated with various root positions suggest that neither the subg. Idria branch nor the subg. Bronnia branch act as long-branch attractors, whereas the branch between the succulent and woody taxa may attract other long branches (Table 4). The root placement in trees resulting from the analyses including outgroup taxa (Fig. 2, analysis 2) does not, therefore, appear to be a result of long-branch attraction. Because the root placement within Fouquieriaceae is uncertain, the implications of all reasonable root positions will be addressed in discussion of character evolution.
Succulent and woody habits
Whether the ancestral condition in Fouquieriaceae is succulent or woody is equivocal, in part due to uncertainty about rooting of the ingroup tree topology and identity of the closest relatives of the family. If subg. Idria and subg. Bronnia fall on different sides of the basal dichotomy in Fouquieriaceae (e.g., a root as in Fig. 2) then succulence may well be the ancestral condition in the family, assuming monophyly of subg. Fouquieria. This would indicate a reversal to the woody condition in subg. Fouquieria. A transition from a succulent habit to a woody habit would be unusual, if not unique. In Cactaceae, the woody Pereskioideae appear to be basal (Hershkovitz and Zimmer, 1997
, citing others), with succulence perhaps achieved via a neotenic reduction of wood developmental rates (Altesor, Silva, and Ezcurra, 1994
). Sufficient phylogenetic information is lacking to assess the direction of life-form evolution in other groups containing both succulent and woody members (e.g., Euphorbiaceae, Asclepiadaceae, and Asteraceae). If the root within Fouquieriaceae falls as suggested above, a woody or an intermediate ancestral condition rather than a succulent condition would dictate independent elaboration of succulence in the three subgenera of Fouquieria: cortical succulence in subg. Fouquieria and stem succulence in both subg. Bronnia and subg. Idria. The woody species of subgenus Fouquieria possess a cortical network of water storage tissue (Scott, 1932
) that is slightly more developed than that of the stem succulents (Humphrey, 1935
; Henrickson, 1969c
). Succulence in both subg. Idria and subg. Bronnia is due to parenchymatous water storage cells within the xylem (Humphrey, 1935
; Henrickson, 1969c
), originating from both cambial division and division of pre-existing parenchymatous cells (Henrickson, 1969c
). Succulent tissue is most extensive in F. columnaris (subg. Idria), which possesses a succulent pith, less extensive in F. purpusii, and least extensive in F. fasciculata (Henrickson, 1969b
, c
, 1972
). If subg. Bronnia is sister to subg. Idria (i.e., a root as in Fig. 4), this would suggest a single origin of stem succulence in Fouquieriaceae and an equivocal ancestral habit in the family.
Determining the direction of evolution between ocotillo and dendroid growth forms relies on resolution of relationships within subg. Fouquieria. Parsimony analysis indicates paraphyly of sect. Fouquieria and derivation of the ocotillo growth form from dendroid forms (Fig. 1). However, ML analyses indicate paraphyly of sect. Ocotilla and derivation of dendroid growth forms from ocotillo forms (Fig. 3). More data on relationships among the members of subg. Fouquieria are needed to resolve life-form evolution in the group.
Polyploidy
Polyploids within Fouquieria include the tetraploid F. diguetii (n = 24) and the hexaploids F. burragei (n = 36) and F. columnaris (n = 36). Henrickson (1972)
suggested that F. diguetii may have descended directly from "F. macdougalii stock" and that F. burragei is perhaps an amphiploid derivative of F. diguetii and another, possibly extinct taxon. Fouquieria macdougalii and F. diguetii share similar floral and inflorescence structure (Henrickson, 1969b
, 1972
). Fouquieria macdougalii (n = 12) is distributed in portions of the Sonoran desert and adjacent tropical deciduous and thorn forests in mainland Mexico (Henrickson 1969b
, 1972
). Fouquieria diguetii is found in Baja California, but overlaps with the range of F. macdougalii around Guaymas, in mainland Mexico (Henrickson, 1969b
, 1972
). The molecular data shown here indicate a close relationship between F. diguetii and F. macdougallii that is consistent with (but not directly supportive of) Henrickson's interpretation of a progenitor–derivative relationship between F. macdougalii and F. diguetii.
Fouquieria burragei is vegetatively very similar to F. macdougalii and, especially, F. diguetii, but is very different in floral characteristics from the two species, with more open flowers, more numerous stamens, pink to white corolla pigmentation (vs. red), and more elongate inflorescences (Henrickson, 1969b
, 1972
). Samples of F. burragei fall in two places in the molecular trees: one with F. diguetii in the parsimony and ML trees and the other with the ocotillo clade (F. splendens and F. shrevei) in the parsimony trees or within the ocotillo grade in the ML trees. Different phylogenetic placements of F. burragei ITS sequences might be the result of bidirectional concerted evolution (Wendel, Schnabel, and Seelanen, 1995
), i.e., different populations of F. burragei may have become fixed for different ITS repeat types inherited from the two parental taxa involved in its putative allopolyploid origin. This interpretation is consistent with Henrickson's (1972)
hypothesis that F. diguetii served as one parent to F. burragei, while a species similar to a white-flowered F. splendens served as the other. Fouquieria burragei is distributed along the eastern coast of lower Baja California (Henrickson, 1969b
, 1972
), overlapping in range with F. diguetii. The current range of F. splendens overlaps with that of F. diguetii on the Baja peninsula, but does not reach quite as far south as the northern known range limit of F. burragei (Henrickson, 1969b
, 1972
). Different subspecies of F. splendens differ in part in floral pigmentation, ranging from red to cream-white, but none of the white forms of F. splendens are known from Baja.
Henrickson's (1972)
suggestion that a representative from the Fouquieria purpusii and F. fasciculata lineage may have served as a parent in the amphiploid derivation of F. columnaris is neither supported nor refuted here, but can be reconciled with our results most easily if the ingroup root falls between the woody and succulent species. Fouquieria purpusii and F. fasciculata (subg. Bronnia) share with F. columnaris (subg. Idria) both vegetative and floral features, including succulent trunks and white to cream-white decandrous flowers (Henrickson, 1972
). Fouquieria columnaris is found in central Baja California and as a small population at Punta Cirio in Sonora, Mexico (Henrickson, 1969b
, 1972
; Humphrey and Marx, 1980
); Fouquieria fasciculata and F. purpusii are highly restricted, found in pockets of arid tropical scrub vegetation (Henrickson, 1972
) in Hidalgo (F. fasciculata) and in Puebla and Oaxaca (F. purpusii)(Henrickson, 1969b
, 1972
). Extensive molecular divergence between these two species and F. columnaris corresponds with their highly disjunct distributions in suggesting that a direct ancestor–descendent relationship between subg. Bronnia and subg. Idria is untenable. A possibility that cannot be discounted is that F. columnaris is an allopolyploid involving a member of subg. Bronnia and an extinct taxon, with the ITS repeat type sequenced from F. columnaris derived from the extinct taxon.
Floral features
While Henrickson did not mention floral pigmentation in his assessment of ancestral features within the family, a root placement along the branch between subg. Fouquieria and the remaining taxa (the root most consistent with Henrickson's hypothesis that F. leonilae and F. ochoterenae are best representative of ancestral conditions within the family) suggests a shift from white/cream floral pigmentation to red pigmentation in ML trees (Figs. 3–4), but is equivocal in parsimony trees (Fig. 1). If subg. Idria and subg. Bronnia fall on opposite sides of the basal dichotomy, white- to cream-colored flowers appear ancestral in the family, with a single derivation of red pigmentation in subg. Fouquieria and, in the parsimony trees (Fig. 1), a reversal(s) in the clade containing F. burragei, F. shrevei, and F. splendens.
While shifts in floral pigmentation and shape may be indicative of pollinator shifts, there does not appear to be strict conformity to stereotypical pollination syndromes within Fouquieriaceae. A temporal match between hummingbird migrations and flowering time in red-flowered F. splendens has been shown to favorably affect seed set (Waser, 1979
). However, carpenter bees are also important pollinators and can be the most frequent visitors (Scott, Buchmann, and O'Rourke, 1993
). Similarly, while 15 species of bees have been observed to visit the white/cream flowered F. columnaris, observed visitors to the white/cream flowered F. fasciculata include hummingbirds, bees, and various other insects (Henrickson, 1972
). In general, observations of pollination in Fouquieriaceae are limited.
Biogeography
Most species of Fouquieriaceae are endemic to mainland Mexico. Those found outside of mainland Mexico (i.e., in Baja California and the southwestern United States) are all polyploid, with the exception of the widespread Fouquieria splendens. While F. diguetii (tetraploid) and F. burragei (hexaploid) are closely related, the two hexaploids F. columnaris and F. burragei, although geographically proximal to one another, must represent independent origins of the hexaploid condition. The overall distribution of Fouquieria species, with all but one diploid species endemic to mainland Mexico, suggests a mainland Mexican origin for the family.
The highly localized distribution of many species (e.g., F. shrevei, F. leonilae, F. ochoterenae, F. fasciculata, F. purpusii) may be indicative of relictualism or neoendemism. Considering the magnitude of the disjunction between the hexaploid F. columnaris and the morphologically similar species of subg. Bronnia it seems likely that considerable extinction has occurred in the history of Fouquieriaceae. This impression is reinforced by the isolation of each of the three subgenera on long branches of the clock-like ITS trees (e.g., Fig. 4).
Concluding remarks
Any discussion of character evolution depends on an accurate tree topology and an accurate placement of a root within that topology. Rooting using an outgroup comparison method is problematic when sister taxa are too divergent or unknown. Outgroup taxa that are too divergent from the ingroup effectively act as random sequences and tend to root an ingroup topology along the longest branch (Wheeler, 1990
). Due to its uncertain phylogenetic placement and its apparently high divergence from other angiosperm taxa, rooting Fouquieriaceae with the outgroup method is problematic, but this problem is certainly not unique.
Our strategy for identifying a root in Fouquieriaceae was to employ the outgroup method using only the conservative (alignable) regions within the outgroup sequences while retaining all ingroup sequence data (Bruns et al., 1992
), a strategy shown to be preferable to retention of all data when portions of the data are highly variable (Smith, 1994
). We rejected the possibility that the root placement resulting from the outgroup method was confounded by long-branch attraction (Huelsenbeck, 1997
). Additionally, we found only three root placements consistent with clock-like evolution of ITS sequences.
Our discussion of character evolution within Fouquieriaceae is based on a set of tree topologies and root placements that appear to be the best hypotheses given the limitations of our data. Future examination of additional morphological and molecular evidence may allow further refinement of our understanding of diversification in this fascinating family.
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FOOTNOTES |
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LITERATURE CITED |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Altesor A., C. Silva, and E. Ezcurra. 1994 Allometric neoteny and the evolution of succulence in cacti. Botanical Journal of the Linnean Society 114: 282–292.
Anderberg, A. A. 1992 The circumscription of the Ericales, and their cladistic relationships to other families of "higher" dicotyledons. Systematic Botany 17: 660–675.[CrossRef][ISI]
Baldwin, B. G. 1992 Phylogenetic utility of the internal transcribed spacers of nuclear ribosomal DNA in plants: an example from the Compositae. Molecular Phylogenetics and Evolution 1: 3–16.[CrossRef][Medline]
Bessey, C. E. 1915 The phylogenetic taxonomy of flowering plants. Annals of the Missouri Botanical Garden 2: 109–164.[CrossRef]
Bruns, T. D., R. Vilgalys, S. M. Barns, D. Gonzalez, D. S. Hibbett, D. J. Lane, L. Simon, S. Stickel, T. M. Szaro, W. G. Weisburg, and M. S. Sogin. 1992 Evolutionary relationships within the fungi: analyses of nuclear small subunit rRNA sequences. Molecular Phylogenetics and Evolution 1: 231–241.[CrossRef][Medline]
Cantino, P. D., R. G. Olmstead, and S. J. Wagstaff. 1997 A comparison of phylogenetic nomenclature with the current system: a botanical case study. Systematic Biology 46: 313–331.[CrossRef]
Cronquist, A. 1981 An integrated system of classification of flowering plants. Columbia University Press, New York, NY.
Dahlgren, R., S. Jensen, and B. Nielsen. 1976 Iridoid compounds in Fouquieriaceae and notes on its possible affinities. Botaniska notiser 129: 207–212.[ISI]
DeCandolle, A. P. 1828 Prodromus Systematis Naturalis Regni Vegetabilis, vol. 3. Treuttel and Wurtz, Paris.
Doyle, J. J., and J. L. Doyle. 1987 A rapid DNA isolation procedure for small quantities of fresh leaf tissue. Phytochemical Bulletin 19: 11–15.
Felsenstein, J. 1988 Phylogenies from molecular sequences: inferences and reliability. Annual Review of Genetics 22: 521–565.[CrossRef][ISI][Medline]
Henrickson, J. 1967 Pollen morphology of the Fouquieriaceae. Aliso 6: 137–160.
———. 1969a Anatomy of periderm and cortex of Fouquieriaceae. Aliso 7: 97–126.
———. 1969b An introduction to the Fouquieriaceae. Cactus and Succulent Journal 61: 97–106.
———. 1969c The succulent Fouquierias. Cactus and Succulent Journal 61: 178–184.
———. 1972 A taxonomic revision of Fouquieriaceae. Aliso 7: 439–537.
Hershkovitz, M. A., and E. A. Zimmer. 1997 On the evolutionary origins of the cacti. Taxon 46: 217–232.[CrossRef][ISI]
Higgins, D. G. 1994 CLUSTAL V: multiple alignment of DNA and protein sequences. In A. M. Griffin and H. G. Griffin [eds.], Computer analysis of sequence data, part II. Methods in molecular biology, vol. 25, 307–318. Humana Press, Totowa, NJ.
Huelsenbeck, J. P. 1997 Is the Felsenstein zone a fly trap? Systematic Biology 46: 69–74.[CrossRef][ISI][Medline]
———, and B. Rannala. 1997 Phylogenetic methods come of age: testing hypotheses in an evolutionary context. Science 276: 227–232.
Hufford, L. 1992 Rosidae and their relationships to other nonmagnoliid dicotyledons: a phylogenetic analysis using morphological and chemical data. Annals of the Missouri Botanical Garden.79: 218–248.
Humboldt, A., A. Bonpland, and C. S. Kunth. 1823 Nova Genera et Species Plantarum, vol. 6. Gide, Paris.
Humphrey, R. R. 1935 A study of Idria columnaris and Fouquieria splendens. American Journal of Botany 22: 184–206.[CrossRef]
———, and D. B. Marx. 1980 Distribution of the boojum tree (Idria columnaris) on the coast of Sonora, Mexico as influenced by climate. Desert Plants 2: 183–187.
Hutchinson, J. 1926 The families of flowering plants I. dicotyledons. MacMillan and Co., London.
Jensen, S. R., and B. J. Nielsen. 1982 Iridoid glucosides in Fouquieriaceae. Phytochemistry 21: 1623–1629.[ISI]
Lledó, M. D., M. B. Crespo, K. M. Cameron, M. F. Fay, and M. W. Chase. 1998 Systematics of Plumbaginaceae based upon cladistic analysis of rbcL sequence data. Systematic Botany 23: 21–29.
Mabry, T. J. 1977 The order Centrospermae. Annals of the Missouri Botanical Garden 64: 210–220.[CrossRef][ISI]
Maddison, W. P., and D. R. Maddison. 1992 MacClade: analysis of phylogeny and character evolution, ver. 3.0. Sinauer, Sunderland, MA.
Markos, S. E. 1995 Phylogeny of Arctostaphylos hookeri (Ericaceae) based on ribosomal DNA sequence from the ITS region. M. A. thesis, San Francisco State University. San Francisco, CA.
Morton, C. M., M. W. Chase, K. A. Kron, and S. M. Swensen. 1996 A molecular evaluation of the monophyly of the order Ebenales based upon rbcL sequence data. Systematic Botany 21: 567–586.[CrossRef][ISI]
Nash, G. V. 1903 A revision of the family Fouquieriaceae. Bulletin of the Torrey Botanic Club 30: 449–459.
Olmstead, R. G., B. Bremer, K. Scott, and J. D. Palmer. 1993 A parsimony analysis of the Asteridae sensu lato based on rbcL sequences. Annals of the Missouri Botanical Garden 80: 700–722.[CrossRef][ISI]
Porter, J. M. 1996 Phylogeny of Polemoniaceae based on nuclear ribosomal internal transcribed spacer DNA sequences. Aliso 15: 57–77.
Roemer, J. J., and J. A. Schultes. 1819 Systema Vegetabilium, vol. 4. Stuttgardt.
Scogin, R. 1977 Anthocyanins of Fouquieriaceae. Biochemical Systematics and Ecology 5: 265–267.[CrossRef]
Scott, F. M. 1932 Some features of the anatomy of Fouquieria splendens. American Journal of Botany 19: 673–678.[CrossRef]
Scott, P. E., S. L. Buchmann, and M. K. O'Rourke. 1993 Evidence for mutualism between a flower-piercing carpenter bee and ocotillo: use of pollen and nectar by nesting bees. Ecological Entomology 18: 234–240.
Smith, A. B. 1994 Rooting molecular trees: problems and strategies. Biological Journal of the Linnean Society 51: 279–292.[CrossRef]
Swofford, D. L. 1993 PAUP: phylogenetic analysis using parsimony, version 3.1. Computer program distributed by the Illinois Natural History Survey, Champaign, IL.
Takhtajan, A. 1969 Flowering plants: origin and dispersal. Smithsonian Institution Press, Washington DC.
Thorne, R. F. 1969 Synopsis of a putatively phylogenetic classification of the flowering plants. Aliso 6: 57–66.
Waser, N. M. 1979 Pollinator availability as a determinant of flowering time in ocotillo (Fouquieria splendens). Oecologia 39: 107–121,[CrossRef][ISI]
Wendel, J. F., A. Schnabel, and T. Seelanan. 1995 Bidirectional interlocus concerted evolution following allopolyploid speciation in cotton (Gossypium). Proceedings of the National Academy of Sciences, USA 92: 280–284.
Wheeler, W. C. 1990 Nucleic acid sequence phylogeny and random outgroups. Cladistics 6: 363–367.
White, T. J., T. Bruns, S. Lee, and J. Taylor. 1990 Amplification and direct sequencing of fungal ribosomal RNA genes for phylogenetics. In M. Innis, D. Gelfand, J. Sninsky, and T. White [eds.], PCR protocols: a guide to methods and applications, 315–322. Academic Press, San Diego, CA.
Wiggins, I. L. 1980 Flora of Baja California. Stanford University Press, Stanford, CA.
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