Biological Journal of the Linnean Society
, 2003,
80
, 261–268. With 2 figures
© 2003 The Linnean Society of London,
Biological Journal of the Linnean Society,
2003,
80
, 261–268
261
Blackwell Science, LtdOxford, UKBIJBiological Journal of the Linnean Society0024-4066The Linnean Society of London, 2003? 2003802261268Original Article
CAM IN PITCAIRNIOIDEAEF. REINERT
ET AL.
*Corresponding author. E-mail: [email protected]
The evolution of CAM in the subfamily Pitcairnioideae (Bromeliaceae)
FERNANDA REINERT
1
, CLAUDIA A. M. RUSSO
2
* and LEANDRO O. SALLES
3
1
Departamento de Botânica, Instituto de Biologia, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
2
Departamento de Genética, Instituto de Biologia, Centro de Ciências da Saúde, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ 21541–570, Brazil
3
Departamento de Vertebrados, Museu Nacional, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
Received 28 August 2002; accepted for publication 7 March 2003
A molecular phylogeny for the subfamily Pitcairnioideae was inferred to examine the distribution of crassulaceanacid metabolism in the subfamily. For this purpose, a neighbour-joining tree with p-distances was built using a
MatK
chloroplast gene data set. The phylogenetic results of our analysis confirmed the monophyletic condition of most gen-era examined:
Brocchinia
,
Dyckia
,
Encholirium
,
Fosterella
,
Hechtia
and
Puya
. A paraphyletic basal sequence showed
Hechtia
branching off from the basal node, followed by
Brocchinia
,
Cottendorfia
+
Navia phelpsiae,
and
Puya
. Theremaining taxa were divided into two groups: (a)
Deuterocohnia meziana
,
Dyckia
,
Encholirium
;
Fosterella
;
Deutero-cohnia
spp.
+
Pitcairnia heterophyla
; (b)
Pepinia
,
Pitcairnia
spp. and
Navia igneosicola
. The basal placement of theCAM genera
Hecthia
indicates that CAM may be a ‘primitive condition’ in Pitcairnioideae and that C
3
species mayhave lost the ability to induce CAM. In this molecular tree, CAM metabolism appeared scattered throughout the tree.Current knowledge, however, does not exclude the possibility that CAM arose only once and it has been switchingon and off in various lineages. Further detailed studies on photosynthetic metabolisms and the phylogenetic distri-bution of characters will provide a better basis on which to evaluate photosynthetic origins. © 2003 The LinneanSociety of London,
Biological Journal of the Linnean Society
, 2003,
80
, 261–268.
ADDITIONAL KEYWORDS:
chloroplast gene
MatK
– molecular systematics – photosynthetic metabolic
pathways – plant phylogeny.
INTRODUCTION
Crassulacean acid metabolism (CAM) is a metabolicpathway found in the photosynthetic tissues of someplants. At night CAM plants take up CO
2
which isfixed into malate via phosphoenolpyruvate carboxy-lase (PEPC). During the day, malate is decarboxylatedand the CO
2
is used in the C
3
pathway (photosyntheticcarbon reduction cycle). CAM-type PEPC is quite dif-ferent from C
3
and C
4
types. For instance, the V
max
ofCAM-type PEPC is C
4
-like but its relatively low K
m
isC
3
-like (Leegood, 1993). Furthermore, CAM-typePEPC is a tetramer whereas the C
4
type is a dimer,
which may account for its lower sensitivity to malateinhibition and to pH variation (Wedding, Black &Meyer, 1990).
During CAM circadian cycles, PEPC is activated bykinase phosphorylation while higher levels of PEPCand PEPC-mRNA regulate CAM metabolism duringtransition from C
3
to CAM in intermediate plants(Ting
et al.
, 1993). CAM plants minimize water lossthrough evaporation by opening their stomata mostlyat night, differing from C
3
and C
4
species. Thus, when-ever water supply is low or day-time temperatures arehigh, CAM plants have an enormous physiologicaladvantage over C
3
and C
4
plants.In the plant kingdom, CAM is widely and discontin-
uously distributed. More than 10% of all vascular
262
F. REINERT
ET AL
.
© 2003 The Linnean Society of London,
Biological Journal of the Linnean Society,
2003,
80
, 261–268
plant species, including monocots, dicots and somepteridophytes (e.g.
Isoetes
and
Pyrrosia
) are constitu-tive CAM or, alternatively, they may engage CAMwhen under hydric or salinic stress (Ting, 1985; Grif-fiths, 1988; Ueno
et al.
, 1988; Cushman & Bohnert,1997). Given the wide and discontinuous distributionof CAM, it has been hypothesized that independentevolutionary events are responsible for the multipleappearances of CAM in land plants (Medina, 1974;Winter & Smith, 1996; Guaralnick & Jackson, 2001);likewise this has been reported for the C
4
pathway(Ehleringer, Cerling & Helliker, 1997; Kellog, 2000;Guaralnick & Jackson, 2001).
In a recent study based on molecular phylogeneticanalyses, various independent appearances of theCAM pathway in the family Portulacaceae werereported (Guaralnick & Jackson, 2001). It remainsunclear, however, if independent appearances arewidespread in plants and, if so, how such a complexmetabolism reappeared so many times in the course ofplant evolution.
The family Bromeliaceae is of major ecologicalimportance in the neotropics and comprises about2600 species divided into 56 genera (Horres
et al.
,2000). Based on floral, fruit and seed characters, thesegenera are assigned to three subfamilies: Pitcairnio-ideae, Tillandsioideae and Bromelioideae. Interest-ingly, several seemingly related bromeliacean generashow considerable variation in their photosyntheticmetabolism, which makes this family particularlyappropriate for a case study on CAM evolution(Medina, 1974). We started our study on the evolutionof CAM metabolism in Bromeliaceae with the subfam-ily Pitcairnioideae.
MATERIAL AND METHODS
We were primarily concerned with the distribution ofCAM in the Pitcairnioideae subfamily. For this, weselected the
MatK
(chloroplast maturase) genesequences available at GenBank (http://www.ncbi.nlm.nih.gov) for members of this bromeliad sub-family. Eleven pitcairnioid genera were included in theanalysis. Most of these were represented by more thanone species, allowing their monophyly to be tested andbringing the total to 35 pitcairnioid species sampled.Since monophyly of Pitcairnioideae has been ques-tioned previously (Terry, Brown & Olmstead, 1997;Horres
et al.
, 2000), we decided to select an outgroupfrom the Rapateaceae Family,
Epidryos,
for our phylo-genetic analysis. The 36 species along with their Gen-Bank accession numbers are listed in Table 1.Photosynthetic pathways were determined from pre-viously published literature (Martin, 1994). When thespecies metabolism was not described, the photosyn-thetic metabolism assigned for the genus was assumed.
Multiple sequence alignments were performed byClustalW available at web site http://www.ebi.ac.uk/clustalw (Higgins
et al.
, 1994). The phylogeneticanalysis of molecular data was carried out withMEGA 2.1, available at http://www.megasoftware.net (Kumar
et al.
, 2001). All base positions thatshowed indels (insertion/deletion events) in thealignment were excluded from the entire phyloge-netic analysis. The
MatK
chloroplast gene data setcomprises 848 base pairs (282 codons) of which only87 sites were variable. The GC content was consis-tently low among species (T: 38%; C: 17%; A: 31%;G: 14%).
Table 1.
GenBank accession numbers for species of thefamily Bromeliaceae used in this study
Family Species nameAccessionno.
Bromeliaceae (Pitcairnioideae)
Brocchinia acuminata
AF162228
Brocchinia micrantha
AF162229
Cottendorfia florida
AF162230
Deuterocohnia longipetala
AF162231
Deuterocohnia lotteae
AF162232
Deuterocohnia meziana
AF162233
Deuterocohnia
sp. AF162226
Dyckia dawsonii
AF162234
Dyckia ferox
AF162235
Dyckia
sp. AF162236
Encholirium irwinii
AF162237
Encholirium inerme
AF162239
Encholirium
sp. AF162238
Fosterella elata
AF162240
Fosterella penduliflora
AF162241
Fosterella petiolata
AF162242
Hechtia glabra
AF162244
Hechtia glomerata
AF162245
Hechtia guatemalensis
AF162246
Hechtia lindmanioides
AF162247
Navia igneosicola
AF162248
Navia phelpsiae
AF162249
Pepinia beachiae
AF162251
Pepinia corallina
AF162252
Pepinia sprucei
AF162253
Pitcairnia heterophylla
AF162254
Pitcairnia orchidifolia
AF162255
Pitcairnia recurvata
AF162256
Pitcairnia rubronigriflora
AF162257
Pitcairnia smithiorum
AF162258
Pitcairnia squarrosa
AF162259
Puya aequatorialis
AF162260
Puya humilis
AF162261
Puya laxa
AF162262
Puya werdermannii
AF162263Rapateaceae
Epidryos allenii
AF162225
CAM IN PITCAIRNIOIDEAE
263
© 2003 The Linnean Society of London,
Biological Journal of the Linnean Society,
2003,
80
, 261–268
The neighbour-joining method of Saitou & Nei(1987) was used to build the phylogenetic tree. Dis-tance methods, such as neighbour-joining, use a spe-cific statistical model to estimate the number ofdifferences between sequences (Russo, Miyaki &Pereira, 2001). Whenever p-distances (i.e. number ofbase differences divided by total number of bases com-pared) are high, there can be a serious underestima-tion of the true evolutionary distance betweenlineages (Nei & Kumar, 2000 and references therein).In such cases, a proper correction model must beapplied so that unbiased estimates are used to con-struct an accurate tree (Rzhetsky & Nei, 1993). How-ever, in our data set, p-distances were small (
<
0.05)and, thus we decided to use them since they have thesmallest variance (Russo, Takezaki & Nei, 1996;Russo
et al.
, 2001). The robustness of the molecularphylogenetic tree was tested with the confidence prob-ability (Rzhetsky & Nei, 1992) test for the neighbour-joining tree. This test has been shown to be a reliableindicator of the accuracy of the tree (Sitnikova,Rhzetsky & Nei, 1995; Russo, 1997).
RESULTS AND DISCUSSION
P
ITCAIRNIOID
PHYLOGENETICS
We used a molecular data set to produce a pitcairnioidphylogeny based on the
MatK
chloroplast gene. Thepairwise p-distance matrix (Table 2) was used to con-struct the neighbour-joining tree (Fig. 1). Mostpitcairnioid genera were monophyletic, namely: Broc-chinia (represented by B. acuminata, B. micrantha),Dyckia (D. dawsonii, D. ferox, D. sp.), Encholirium(E. inerme, E. irwinii, E. sp.), Fosterella (F. elata,F. penduliflora, F. petiolata), Hechtia (H. glabra,H. glomerata, H. guatemalensis, H. lindmanioides)and Puya (P. aequatorialis, P. humilis, P. laxa,P. werdermannii).
Our phylogenetic analysis also showed that the fol-lowing genera were not monophyletic: Deuterocohnia(D. longipetala, D. lotteae, D. meziana, D. sp.), Navia(N. igneosicola, N. phelpsiae), Pepinia (P. beachiae,P. corallina, P. sprucei) and Pitcairnia (P. hetero-phylla, P. orchidifolia, P. recurvata, P. rubronigriflora,P. smithiorum, P. squarrosa). The genus Cottendorfiawas represented by a single species. In order to makethe text more readable, we will henceforth refer to themonophyletic genera simply by the genus name; theothers will be referred to by the name of the outlierspecies and ‘Genus spp.’ will refer to the remainingspecies of the genus.
The first division in Pitcairnioideae was when Hech-tia separated from the remaining pitcairnioidean spe-cies and Brocchinia was placed inside the main group(Fig. 1). Our result contrasts with a recent phyloge-netic study in which a molecular tree shows Broc-
chinia as the basal clade and Hechtia as the second tosplit (Horres et al., 2000). In that study, pitcairnioide-ans were not grouped in a monophyletic clade, andBrocchinia appeared separately from other pitcairnio-idean species as the most basal genus for the familyBromeliaceae. Another study also placed Brocchiniaas basal among bromeliaceans (Terry et al., 1997).Unfortunately, these authors did not include Hechtiain their study, making a useful comparison betweenour study and theirs difficult.
One could argue that rooting preferences mightaccount for the differences observed among the threestudies. Nonetheless, our phylogenetic tree was rootedwith Epidryos, a member of the Rapateaceae family.Since the monophyletic status of the Bromeliaceaefamily has been ascertained (Terry et al., 1997; Horreset al., 2000), an error as a result of our rooting pref-erence is thus excluded. It should be noted that in thestudies of Terry et al. (1997), Horres et al. (2000) andhere, statistical support for the nodes were relativelylow, indicating that more data are necessary in orderto resolve this matter.
After the divergence of Hechtia, the next groupingin the tree in Figure 1 shows an unresolved trichot-omy with Brocchinia, Navia + Cottendorfia and theremaining species. Puya spp. separated basally fromthe remaining species which were, in turn, dividedinto two main groups. The first group divided intothree different subgroups: the sister genera (Dyckia,Encholirium) tightly joined (99%) with Deuterocohniameziana; Fosterella spp.; Pitcairnia heterophylla+ Deuterocohnia spp.
In the second main group, the remaining Pitcairniaspp. were clustered as a paraphyletic sequence thatincluded Pepinia spp., with Navia igneosicola diverg-ing basally from them. It seems clear that Pitcairniaheterophylla should be considered as belonging to adifferent genus from the remaining species(Fig. 1), probably along with P. loki-schmidtii andP. pseudopungens (Horres et al., 2000). Another molec-ular study in Bromeliaceae with ndhF chloroplastgene sequences (Terry et al., 1997) also joins Pepiniaand Pitcairnia. In fact, Pepinia used to be assigned asa subgenus of Pitcairnia, but it was raised to genericstatus by a morphological analysis (Varadarajan &Gilmartin, 1988a). In our tree, these genera clusteredwith a relatively high CP value (86%) suggesting thatthe condition of Pitcairnia and Pepinia as separategenera must be re-evaluated. As a matter of fact, arecent review listed all Pepinia species examined here(P. beachiae, P. corallina, P. sprucei) within the genusPitcairnia (Taylor & Robinson, 1999).
Navia igneosicola was the basal species in the sec-ond major group, outside the Pitcairnia + Pepiniaclade, and was placed in a separate branch from thecongeneric N. phelpsiae. Besides Pitcairnia and Pep-
264 F. REINERT ET AL.
© 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 80, 261–268
Tab
le 2
.M
atK
ch
loro
plas
t ge
ne
pair
wis
e p-
dist
ance
s (¥
1000
) fo
r al
l pi
tcar
inio
idea
n (
Bro
mel
iace
ae)
spec
ies
com
pari
son
s pl
us
the
outg
rou
p E
pid
ryos
(R
apat
acea
e)
12
34
56
78
910
1112
1314
1516
1718
1920
2122
2324
2526
2728
2930
3132
3334
3536
1B
rocc
hin
ia a
cum
inat
a2
Bro
cch
inia
mic
ran
tha
93
Cot
ten
dor
fia
flor
ida
2622
4D
eute
roco
hn
ia lo
ngi
peta
la28
2720
5D
eute
roco
hn
ia l
otte
ae27
2619
46
Deu
tero
coh
nia
mez
ian
a28
2722
1816
7D
eute
roco
hn
ia s
p.28
2420
34
188
Dyc
kia
daw
son
ii31
3024
2019
320
9D
ycki
a fe
rox
3130
2420
193
203
10D
ycki
a sp
.31
3024
2019
320
03
11E
nch
olir
ium
in
erm
e30
2823
1918
119
14
112
En
chol
iriu
m i
rwin
ii30
2823
1918
119
14
10
13E
nch
olir
ium
sp.
3635
3026
248
268
118
77
14F
oste
rell
a el
ata
3028
2322
2018
2220
2020
1919
2615
Fos
tere
lla
pen
du
lifl
ora
4238
3127
2628
2731
3131
3030
3623
16F
oste
rell
a pe
tiol
ata
2827
2019
1818
1920
2020
1919
265
2017
Hec
hti
a gl
abra
2824
1822
2023
2226
2626
2424
2822
3019
18H
ech
tia
glom
erat
a24
2013
1816
1918
2222
2220
2024
1826
154
19H
ech
tia
guat
emal
ensi
s24
2013
1816
1918
2222
2220
2024
1826
159
520
Hec
hti
a li
nd
man
ioid
es28
2418
2220
2322
2626
2624
2428
2230
190
49
21N
avia
ign
eosi
cola
2627
2016
1518
1620
2020
1919
2622
3019
2218
1822
22N
avia
ph
elps
iae
2624
1219
1820
1923
2323
2222
2822
3219
1915
1519
1923
Pep
inia
bea
chia
e24
2319
1816
1818
2020
2019
1926
1831
1820
1616
2012
1624
Pep
inia
cor
alli
na
2423
1918
1618
1820
2020
1919
2618
3118
2016
1620
1216
025
Pep
inia
spr
uce
i24
2319
1816
1818
2020
2019
1926
1831
1820
1616
2012
160
026
Pit
cair
nia
het
erop
hyl
la27
2718
1615
2016
2323
2322
2228
2230
1922
1818
2218
1918
1818
27P
itca
irn
ia o
rch
idif
olia
2423
1918
1618
1820
2020
1919
2319
3118
1813
1318
1216
55
518
28P
itca
irn
ia r
ecu
rvat
a26
2420
1918
1919
2222
2220
2027
2032
1920
1618
2013
187
77
197
29P
itca
irn
ia r
ubr
onig
rifl
ora
2423
1918
1618
1820
2020
1919
2618
3118
2016
1620
1216
00
018
57
30P
itca
irn
ia s
mit
hio
rum
2423
1915
1318
1520
2020
1919
2619
3118
2016
1620
1216
33
315
57
331
Pit
cair
nia
squ
arro
sa23
2218
1513
1515
1818
1816
1623
1828
1619
1515
199
154
44
164
54
432
Pu
ya a
equ
ator
iali
s22
1811
1211
1312
1616
1615
1522
1523
1212
88
1212
1211
1111
1211
1211
119
33P
uya
hu
mil
is22
2013
1211
1312
1616
1615
1522
1526
1215
1111
1512
1211
1111
1211
1211
119
334
Pu
ya l
axa
2218
1112
1113
1216
1616
1515
2215
2312
128
812
1212
1111
1112
1112
1111
90
335
Pu
ya w
erd
erm
ann
ii20
1912
119
1211
1515
1513
1320
1324
1113
99
1311
119
99
119
119
98
11
136
Epi
dry
os a
llen
ii90
9086
9089
8890
9090
9089
8993
8892
8684
8080
8489
8485
8585
8984
8585
8582
8284
8282
CAM IN PITCAIRNIOIDEAE 265
© 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 80, 261–268
inia, other pitcairnioidean taxa have consistentlyappeared as sister groups in phylogenetic analyses todate. For instance, the genera (Navia + Cottendorfia)and (Encholirium + Dyckia) are always grouped inmolecular- (Terry et al., 1997; this study) and morphol-ogy-based trees (Varadarajan & Gilmartin, 1988b;Robinson & Taylor, 1999). The generic status of Navia,Pepinia, Pitcairnia and Deuterocohnia should be care-fully reconsidered given that their morphological diag-nostic characters may prove to be convergences ratherthan homologies.
Plant-specific features such as polyploidization, aninstant speciation agent, may facilitate convergentevolution, starting at the molecular level. For thisreason, major events in plant evolution are nowstarting to be re-investigated and molecular tools
are playing a central role in this process (for reviewssee Soltis & Soltis, 2000; Daly, Cameron & Steven-son, 2001). This is happening not only at lower butalso at higher taxonomic levels, whenever homologyhypotheses are difficult to confirm. Obviously, iflower level taxonomy is not well-established, even inimportant families such as Bromeliaceae, there islittle hope for higher level taxonomy in plants. Forinstance, our phylogenetic tree (Fig. 1) does not rein-force tribal subdivisions previously suggested forPitcairnioideae into two (Robinson & Taylor, 1999) orthree (Varadarajan & Gilmartin, 1988a) tribes. Rig-orous statistical tests in molecular systematics, suchas the bootstrap and the confidence probability tests,have proven reliable both in simulations (Sitnikovaet al., 1995) and in empirical tests (Russo, 1997).
Figure 1. Neighbour-joining tree with p-distances for 35 pitcairnioid species for MatK gene sequences. Epidryos (FamilyRapataceae) was used as the outgroup.
Dyckia dawsonii
Dyckia sp.
Dyckia ferox
Encholirium sp.
Encholirium inerme
Encholirium irwinii
Deuterocohnia meziana
CAM
Fosterella penduliflora
Fosterella elata
Fosterella petiolata
C3
C3 Pitcairnia heterophylla
Deuterocohnia lotteae
Deuterocohnia longipetala
Deuterocohnia sp.
CAM
Navia igneosicola
Pitcairnia squarrosa
Pitcairnia orchidifolia
Pitcairnia recurvata
Pitcairnia smithiorum
Pepinia beachiae
Pitcairnia rubronigriflora
Pepinia corallina
Pepinia sprucei
C3
Puya humilis
Puya werdermannii
Puya laxa
Puya aequatorialis
CAM/C3
Cottendorfia florida
Navia phelpsiaeC3
Brocchinia acuminata
Brocchinia micranthaC3
Hechtia guatemalensis
Hechtia glomerata
Hechtia glabra
Hechtia lindmanioides
CAM
Epidryos allenii
99
92
68
73
65
99
69
92
96
85
86
80
99
76
67
86
79
71
68
57 68
70
51
69
64
63
266 F. REINERT ET AL.
© 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 80, 261–268
Such tests are known to distinguish between noiseand phylogenetic signals, and we strongly encour-age their use in plant phylogenetics. Molecular andstatistical tools have great potential to unravel plantphylogenetic relationships, contributing to a betterunderstanding of the origin of the photosyntheticpathways, such as the evolution of CAM.
CAM EVOLUTION
The basal placement of Hechtia (a CAM plant) ratherthan Brocchinia (a C3 plant) suggests that CAMmetabolism is a ‘primitive condition’ for the subfamily(Fig. 1). Clarifying the base of the tree is important ifwe are to understand how CAM has emerged in bro-meliads. If this pattern proves to be correct, it meansthat all C3 pitcairnioidean species have lost the abilityto induce CAM metabolism.
Figure 1 also shows that CAM seems to have origi-nated several times in this subfamily where it appearsscattered throughout the tree, as was reported for thePortulacaceae family (Guaralnick & Jackson, 2001).Nevertheless, if we plot the occurrence of CAM metab-olism in a morphologically based tree, surprisingly,CAM may have arisen only once (Fig. 2 – adapted fromVaradarajan & Gilmartin’s (1988b) data set). Indeed,we notice that, with the exception of Brewcaria, ofunknown photosynthetic pathway, CAM is present ina single clade. Note, however, that the genus Puya hasspecies that exhibit both types of metabolisms (C3 andCAM) and that the photosynthetic mode of some mem-bers is also uncertain.
Given that the two basal genera, namely Glomero-pitcairnia and Brocchinia, display C3 metabolism, theCAM photosynthetic pathway could well be inter-preted as a synapomorphy for the CAM clade in thismorphological analysis, contrary to the patternobserved in the molecular tree. In other words, giventhe distribution of C3 and CAM in the cladogram inFigure 2, it appears that a single evolutionary change
might have produced a shift from C3 to CAM pathwayin Pitcairnioideae. Differences between morphologicaland molecular trees regarding CAM distribution maybe explained by sampling differences in these studiesor by convergent evolution events.
The molecular tree presented here (Fig. 1) suggestsmultiple appearances of CAM in various pitcairnioidlineages. Nevertheless, a single origin of CAM in anancient plant lineage cannot be ruled out. In this sce-nario, CAM has been switching on and off in variouslineages. Biochemically, however, switches in descentlineages seem like an oversimplification because theseplants may show different ‘levels’ of CAM, such asCAM-cycling, CAM-idling and CAM-like (Ting, 1985;Monson, 1989). The expression of CAM in certainplants, such as Mesembryantheumum crystallinumand Guzmania monostachya, can be triggered eitherdevelopmentally or when they are subjected to variousstresses (e.g. water and salt stresses) (Maxwell, 2002;Ting, 1985; Winter & Ziegler, 1992; Saitou et al.,1994).
It has been proposed that all the machinery neces-sary for CAM is available in C3 plants, suggesting thata complex regulatory mechanism plays a key role inthe appearance of CAM (Cushman & Bohnert, 1997).However, the central issue still remains as to whetherCAM represents a single phylogenetic unit. More data,specifically on the promoter region of key enzymes ofCAM, is crucial.
Future avenues of research on the evolution ofphotosynthesis and the mechanisms which optimizecarbon assimilation should integrate two researchlines. The first must concentrate on a detailed andthorough study of the genetics, biochemistry andphysiology behind multiple photosynthetic com-plexes. The second should focus on the phylogeneticdistribution of such complexes. A combination ofthese approaches will provide sound empiricalgrounds for the formulation of hypotheses of photo-synthetic identities and origins.
Figure 2. Maximum parsimony tree for an ecomorphological data set (redrawn from Varadarajan & Gilmartin, 1988b).
Brewcaria Dyckia Encholirium Deuterocohnia Abromeitiella Puya Hechtia
CAM
Steyerbromelia Pitcairnia Pepinia Cottendorfia Ayensua Navia Connelia Fosterella
C3
Brocchinia Glomeropitcairnia
CAM IN PITCAIRNIOIDEAE 267
© 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 80, 261–268
ACKNOWLEDGEMENTS
The authors wish to thank CNPq (Brazilian researchcouncil) and FAPERJ (Rio de Janeiro’s research foun-dation) for research grants, and Andrew Macrae forsuggestions about the manuscript.
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