Phylogeny and circumscription of Sapindaceae revisited: molecular sequence data, morphology and biogeography support recognition of a new family, Xanthoceraceae.

TL;DR: The relationships of Xanthoceras are clarified based on phylogenetic analyses using a dataset encompassing nearly 3/4 of sapindaceous genera, comparing the results with information from morphology and biogeography, and support earlier suggestions that Harpullieae are polyphyletic.

Abstract: Background and aims Recent studies have adopted a broad definition of Sapindaceae that includes taxa traditionally placed in Aceraceae and Hippocastanaceae, achieving monophyly but yielding a family difficult to characterize and for which no obvious morphological synapomorphy exists. This expanded circumscription was necessitated by the finding that the monotypic, temperate Asian genus Xanthoceras, historically placed in Sapindaceae tribe Harpullieae, is basal within the group. Here we seek to clarify the relationships of Xanthoceras based on phylogenetic analyses using a dataset encompassing nearly 3/4 of sapindaceous genera, comparing the results with information from morphology and biogeography, in particular with respect to the other taxa placed in Harpullieae. We then re-examine the appropriateness of maintaining the current broad, morphologically heterogeneous definition of Sapindaceae and explore the advantages of an alternative family circumscription. Methods Using 243 samples representing 104 of the 142 currently recognized genera of Sapindaceae s. lat. (including all in Harpullieae), sequence data were analyzed for nuclear (ITS) and plastid (matK, rpoB, trnD-trnT, trnK-matK, trnL-trnF and trnS-trnG) markers, adopting the methodology of a recent family-wide study, performing single-gene and total evidence analyses based on maximum likelihood (ML) and maximum parsimony (MP) criteria, and applying heuristic searches developed for large datasets, viz, a new strategy implemented in RAxML (for ML) and the parsimony ratchet (for MP). Bootstrap analyses were performed for each method to test for congruence between markers. Key results Our findings support earlier suggestions that Harpullieae are polyphyletic: Xanthoceras is confirmed as sister to all other sampled taxa of Sapindaceae s. lat.; the remaining members belong to three other clades within Sapindaceae s. lat., two of which correspond respectively to the groups traditionally treated as Aceraceae and Hippocastanaceae, together forming a clade sister to the largely tropical Sapindaceae s. str., which is monophyletic and morphologically coherent provided Xanthoceras is excluded. Conclusion To overcome the difficulties of a broadly circumscribed Sapindaceae, we resurrect the historically recognized temperate families Aceraceae and Hippocastanaceae, and describe a new family, Xanthoceraceae, thus adopting a monophyletic and easily characterized circumscription of Sapindaceae nearly identical to that used for over a century.

Summary

Alignment and phylogenetic analyses

• The number of samples and statistics for each partition and the combined data set are summarized in table 2.
• The only exception was the ITS region, in which a proportion of invariable sites was added (GTR+G+I).
• The MP and ML single-gene phylogenies provided different levels of resolution, but no differences with a bootstrap support greater than 75% were identified when compared, so the authors combined them in a total evidence approach.
• For the combined analyses under the MP criterion, nine of the ten independent PAUPrat searches converged on a best score of 11526 steps and produced a total of 949 most parsimonious trees, which were used to compile a strict consensus (not shown); this consensus tree comprised several polytomies, especially near the tips.
• Under the ML criterion, the best-fit model for the combined matrix was GTR+G+I.

Phylogenetic relationships

• With the addition of the ninety ingroup samples used in the present analysis, including representatives of several genera of Sapindaceae s. lat.
• The authors results also indicate that the other genera of Harpullieae belong to three additional clades, one in subfam.
• Sapindoideae (figs 1 & 2), confirming the polyphyly of the tribe.
• The inclusion of Billia and Handeliodendron in their analysis, along with additional species of Acer and Aesculus, strengthens support for the monophyly of both Aceraceae and Hippocastanaceae and confirms their sister relationship (fig. 1A & B).
• Support for the clade comprising Sapindaceae s. str. (i.e. Dodonaeoideae plus Sapindoideae) is likewise stronger in the present analysis (BS = 88) than in that of Buerki et al.

Figures

Table 1 – Characteristics of partitions used in the phylogenetic analyses of Sapindaceae s. lat. IGS = intergenic spacer; MP = maximum parsimony; PI = potentially parsimony informative; CI = constistency index; RI = retention index; 1for No. of sequences, the total number of samples for the combined analyses is indicated between brackets; 2for mean amount of phylogenetic information per sample: averaged by alignment size/variable sites number/PI sites number.

Figure 2 – Relationships within subfamily Sapindoideae. Bootstrap supports are indicated above branches. CUP = Cupanieae; KOE = Koelreuterieae; HAR = Harpullieae; MEL = Melicocceae; NEP = Nephelieae; SCH = Schleichereae. The definition of the groups follows Buerki et al. (2009).

Full text

Plant Ecology and Evolution 143 (2): 148–159, 2010
doi:10.5091/plecevo.2010.437
Phylogeny and circumscription of Sapindaceae revisited:
molecular sequence data, morphology and biogeography
support recognition of a new family, Xanthoceraceae
Sven Buerki
1
, Porter P. Lowry II
2,3,*
, Nadir Alvarez
4
, Sylvain G. Razamandimbison
5
,
Philippe Küpfer
6
& Martin W. Callmander
2,7
1
Department of Biodiversity and Conservation, Real Jardin Botanico, CSIC, Plaza de Murillo 2, ES-28014 Madrid, Spain
2
Missouri Botanical Garden, P.O. Box 299, St. Louis, MO 63166-0299, U.S.A.
3
Muséum National d’Histoire Naturelle, Case Postale 39, 57 rue Cuvier, FR-75231 05 CEDEX, Paris, France
4
Department of Ecology and Evolution, Biophore, University of Lausanne, CH-1015 Lausanne, Switzerland
5
Department of Botany, Bergius Foundation, SE-10691, Stockholm University, Stockholm, Sweden
6
Institute of Biology, University of Neuchâtel, Rue Emile-Argand 11, CH-2000 Neuchâtel, Switzerland
7
Conservatoire et Jardin botaniques de la ville de Genève, ch. de l’Impératrice 1, CH-1292 Chambésy, Switzerland
*Author for correspondence: pete.lowry@mobot.org
All rights reserved. © 2010 National Botanic Garden of Belgium and Royal Botanical Society of Belgium – ISSN 2032-3913
REGULAR PAPER
Background and aims – Recent studies have adopted a broad denition of Sapindaceae that includes
taxa traditionally placed in Aceraceae and Hippocastanaceae, achieving monophyly but yielding a family
difcult to characterize and for which no obvious morphological synapomorphy exists. This expanded
circumscription was necessitated by the nding that the monotypic, temperate Asian genus Xanthoceras,
historically placed in Sapindaceae tribe Harpullieae, is basal within the group. Here we seek to clarify
the relationships of Xanthoceras based on phylogenetic analyses using a dataset encompassing nearly ¾
of sapindaceous genera, comparing the results with information from morphology and biogeography, in
particular with respect to the other taxa placed in Harpullieae. We then re-examine the appropriateness of
maintaining the current broad, morphologically heterogeneous denition of Sapindaceae and explore the
advantages of an alternative family circumscription.
Methods – Using 243 samples representing 104 of the 142 currently recognized genera of Sapindaceae s.
lat. (including all in Harpullieae), sequence data were analyzed for nuclear (ITS) and plastid (matK, rpoB,
trnD-trnT, trnK-matK, trnL-trnF and trnS-trnG) markers, adopting the methodology of a recent family-
wide study, performing single-gene and total evidence analyses based on maximum likelihood (ML) and
maximum parsimony (MP) criteria, and applying heuristic searches developed for large datasets, viz. a new
strategy implemented in RAxML (for ML) and the parsimony ratchet (for MP). Bootstrap analyses were
performed for each method to test for congruence between markers.
Key results – Our ndings support earlier suggestions that Harpullieae are polyphyletic: Xanthoceras is
conrmed as sister to all other sampled taxa of Sapindaceae s. lat.; the remaining members belong to three
other clades within Sapindaceae s. lat., two of which correspond respectively to the groups traditionally
treated as Aceraceae and Hippocastanaceae, together forming a clade sister to the largely tropical Sapin-
daceae s. str., which is monophyletic and morphologically coherent provided Xanthoceras is excluded.
Conclusion – To overcome the difculties of a broadly circumscribed Sapindaceae, we resurrect the his-
torically recognized temperate families Aceraceae and Hippocastanaceae, and describe a new family, Xan-
thoceraceae, thus adopting a monophyletic and easily characterized circumscription of Sapindaceae nearly
identical to that used for over a century.
Key words – Aceraceae, Harpullieae, Hippocastanaceae, molecular phylogeny, new family, Sapindaceae,
Xanthoceras, Xanthoceraceae.

149
Buerki et al., Recognition of a new family, Xanthoceraceae
INTRODUCTION
The systematics of the family Sapindaceae has challenged
taxonomists for more than a century since its rst compre-
hensive treatment was published by Radlkofer (1890, 1933).
Until the late 1980s, Sapindaceae were widely treated as
distinct from two closely related families, Hippocastanaceae
and Aceraceae, based primarily on morphology and bioge-
ography (Takhtajan 1987, Cronquist 1988, Dahlgren 1989).
Several recent studies using pollen morphology (Müller &
Leenhouts 1976), phytochemistry (Umadevi & Daniel 1991)
and molecular sequence data (Gadek et al. 1996, Savolainen
et al. 2000, APG II 2003, APG III 2009, Harrington et al.
2005, Buerki et al. 2009) have, however, led to the adoption
of a broader concept in an effort to ensure monophyly, uniting
these entities into a single family, Sapindaceae s. lat.
Sapindaceae s. lat. as currently circumscribed by Har-
rington et al. (2005), Thorne & Reveal (2007) and Buerki
et al. (2009, 2010) comprise c. 1900 species and 142 genera
distributed among four subfamilies: Dodonaeoideae Burnett,
Hippocastanoideae Burnett, Sapindoideae Burnett and Xan-
thoceroideae Thorne & Reveal. Recently, Buerki et al. (2009)
demonstrated the para-/polyphyly of all tribes as dened by
Radlkofer (1933), with a single exception, Paullinieae Kunth.
Although they sketched an informal system that recognizes a
dozen monophyletic groups, they did not propose new tribal
limits within the four subfamilies as many potentially impor-
tant genera of Sapindaceae were not included in their study
due to the lack of sequenceable material.
Historically, Radlkofer (1933) recognized fourteen tribes
within Sapindaceae s. str., ve in Dodonaeoideae and nine in
Sapindoideae (see table 1 in Buerki et al. 2009 for details).
Within Dodonaeoideae, however, he encountered difculty
assigning nine genera to the four previously described tribes,
ultimately deciding to place them in a new tribe, Harpullieae
Radlk. Within this heterogeneous assemblage, he recognized
two informal groups according to the presence (Delavaya Fran-
chet, Ungnadia Endl. and Xanthoceras Bunge) or absence (Ar-
feuillea Pierre, Conchopetalum, Eurycorymbus Hand.-Mazz.,
Harpullia Roxb., Magonia A.St.-Hil. and Majidea J.Kirk ex
Oliv.) of a terminal leaet. While revising Radlkofer’s infra-
familial system, largely on the basis of pollen and other mor-
phological features, Müller & Leenhouts (1976) discussed the
possible expansion of Harpullieae to include the three genera
comprising Hippocastanaceae, viz. Aesculus L., Billia L. and
Handeliodendron (these authors did not, however, comment on
the taxonomic status of Aceraceae). In their revised classica-
tion, Müller & Leenhouts (1976) concluded that the connection
between Hippocastanaceae and Harpullieae might involve two
genera in particular, Handeliodendron, originally described in
Sapindaceae (Rehder 1935), and Delavaya, which has always
been placed in Sapindaceae. Müller & Leenhouts (1976) also
regarded Harpullieae as a “heterogeneous assemblage”, with
several genera difcult to connect to the others. For example,
they classied Harpullia pollen as both type-A and type-H
and Magonia pollen as type-E, whereas other members of the
tribe exclusively exhibit the more common type-A pollen (see
Buerki et al. 2009 for more details on pollen morphology).
Moreover, Harpullieae range from tropical (e.g. Conchopeta-
lum, Delavaya, Magonia) to temperate (Xanthoceras) regions
and include both evergreen and deciduous species (Radlkofer
1933, Müller & Leenhouts 1976). Based on wood anatomy,
Klaassen (1999) noted a difference between the temperate
and tropical genera in the tribe, and among the tropical ones
he indicated that Delavaya and Ungnadia stood out because
their wood is similar to that of members of tribe Cupanieae
Reichenb. (Sapindoideae). Buerki et al. (2009) found Harpul-
lieae to be polyphyletic, with Xanthoceras occupying a basal
position within Sapindaceae s. lat., Arfeuillea, Eurycorymbus,
Harpullia and Majidea placed in Dodonaeoideae, Delavaya
occupying a basal position within Sapindoideae, and Concho-
petalum resolved in the Macphersonia group (Sapindoideae;
Buerki et al. 2009) closely related to the newly described en-
demic Malagasy genus Gereaua Buerki & Callm. (Buerki et al.
2010). A close relationship between Delavaya and Ungnadia
was found in an earlier cladistic analysis based on morphol-
ogy (Judd et al. 1994), which identied the presence of pro-
longed basal petal appendages and glabrous stamens as puta-
tive synapomorphies, again suggesting that Harpullieae were
far from representing a natural assemblage.
In the present study we seek to (1) clarify the relation-
ships of Xanthoceras within Sapindaceae s. lat. and in particu-
lar with respect to the other taxa traditionally and/or currently
placed in Harpullieae, and (2) re-examine the appropriateness
of maintaining the current broadly circumscribed but mor-
phologically heterogeneous denition of Sapindaceae and
explore the possible advantages of alternative family circum-
scriptions. Toward this end, we have signicantly expanded
the dataset of Buerki et al. (2009) to conduct a new set of
phylogenetic analyses, comparing the results with informa-
tion from morphology and biogeography.
MATERIAL AND METHODS
Sampling, sequence data and phylogenetic analyses
Species names, voucher information, and GenBank accession
numbers for all sequences are provided in the appendix. The
dataset presented in Buerki et al. (2009) was expanded to in-
clude a total of 243 samples encompassing more than 70% of
the generic diversity in Sapindaceae s. lat. (104 of the currently
recognized 142 genera; half of the 38 genera not included in
this analysis are monospecic), representing an increase of
ninety ingroup samples and nineteen genera. To assess the phy-
logenetic relationships of the taxa placed in tribe Harpullieae
and in the traditionally recognized families Aceraceae and Hip-
pocastanaceae, we sampled at least one species from each ge-
nus currently assigned to these groups by adding the following
genera: Magonia and Ungnadia from Harpullieae, plus Billia
and Handeliodendron from Hippocastanaceae (Aesculus, the
third member of this family, was included in the analysis of
Buerki et al. 2009, as were both genera of Aceraceae, Acer and
Dipteronia). The outgroup sampling included one taxon each
from Anacardiaceae (Sorindeia sp., used as the most external
outgroup), Meliaceae (Malleastrum sp.) and Simaroubaceae
(Harrisonia abyssinica Oliv.).
The DNA extraction, amplication and sequencing proto-
cols used for the nuclear and plastid regions are provided in
Buerki et al. (2009). The nuclear sequences include the whole
ITS region (ITS1, 5.8S and ITS2) and plastid markers include

150
Pl. Ecol. Evol. 143 (2), 2010
both coding (matK and rpoB) and non-coding regions (the
trnL intron and the intergenic spacers trnD-trnT, trnK-matK,
trnL-trnF and trnS-trnG).
Single-gene, total evidence analyses and their correspond-
ing bootstrap analyses were performed using the maximum par-
simony (MP) and maximum likelihood (ML) criteria following
the same procedure as in Buerki et al. (2009). Parsimony ratch-
et (Nixon 1999) was performed for each partition and for the
combined data set using PAUPRat (Sikes & Lewis 2001). Ten
independent searches were performed with 200 iterations and
15% of the parsimony informative characters perturbed. A strict
consensus tree was constructed based on the shortest equally
parsimonious trees. To assess support at each node, non para-
metric bootstrap analyses (Felsenstein 1985) were performed
using PAUP* (Swofford 2002) following the same procedure
as in Buerki et al. (2009). Model selection for each partition
was assessed using Modeltest v. 3.7 (Posada & Crandall 1998).
ML analyses were performed using RAxML v. 7.0.0 (Stama-
takis 2006, Stamatakis et al. 2008) with 1000 rapid bootstrap
analyses followed by a search for the best-scoring tree in one
single run. These analyses were done using the facilities made
available by the CIPRES portal in San Diego, USA (http://8ball.
sdsc.edu:8888/cipres-web/home).
Topological differences between single-gene phylogenetic
trees were compared by taking into account the level of resolu-
tion obtained by each marker and its bootstrap support. Topo-
logical differences with bootstrap support (BS) less than 75%
were not considered.
Table 1 – Characteristics of partitions used in the phylogenetic analyses of Sapindaceae s. lat.
IGS = intergenic spacer; MP = maximum parsimony; PI = potentially parsimony informative; CI = constistency index; RI = retention
index;
1
for No. of sequences, the total number of samples for the combined analyses is indicated between brackets;
2
for mean amount of
phylogenetic information per sample: averaged by alignment size/variable sites number/PI sites number.
Single-gene analysis
Phylogenetic
information
ITS matK rpoB
trnD-trnT
IGS
trnK-
matK
IGS
trnL
intron
trnL-
trnF
IGS
trnS-trnG
IGS
8 markers
No. of ingroup
sampled
species/genera
156/89 159/89 174/96 94/69 119/74 169/97 165/93 74/52 214/104
No. sequences
1
172 175 199 102 133 192 189 80 1242 (243)
Sequences: this
study/Genbank
165/5 146/29 199/0 102/0 131/2 188/4 186/3 80/0 -
Sequence
length range
650–705 1074–1242 357–363 1086–1425 705–753 510–522 380–430 1311–1365 -
Alignment
length
1234 1614 363 1925 931 773 661 2156 9657
No. constant
characters (%)
584 1062 222 965 488 454 328 1577 5681
(47.3%) (65.7%) (61.1%) (50.1%) (52.4%) (58.7%) (49.6%) (73.1%) (58.8%)
No. variable
characters (%)
653 552 141 960 443 319 333 579 3976
(52.9%) (34.2%) (38.8%) (49.9%) (47.6%) (41.2%) (50.4%) (26.8%) (41.2%)
No. potentially
PI characters
(%)
491 392 104 505 277 194 217 227 2404
(39.8%) (24.3%) (28.7%) (26.2%) (29.8%) (25.1%) (32.8%) (10.5%) (24.9%)
Mean amount
of phylogenetic
information
per sample
2
- - - - - - - - 16.4/39.7/9.9
No. trees
retained
214 1967 2010 1975 1703 1500 667 1820 949
Tree length
(steps)
4666 1185 281 1858 954 687 705 945 11526
Consistency
Index (CI)
0.272 0.632 0.672 0.694 0.633 0.644 0.646 0.711 0.492
Retention
Index (RI)
0.673 0.860 0.907 0.790 0.775 0.881 0.858 0.650 0.749

151
Buerki et al., Recognition of a new family, Xanthoceraceae
Figure 1 – A, best maximum likelihood phylogenetic tree for Sapindaceae s. lat.; B, relationships between and within Aceraceae and Hippocastanaceae; C, relationships within subfamily
Dodonaeoideae. Bootstrap supports are indicated above branches. COS = Cossinieae; CUP = Cupanieae; DOD = Dodonaeeae; DOR = Doratoxyleae; HAR = Harpullieae. The denition
of the groups follows Buerki et al. (2009).
A
B
C

152
Pl. Ecol. Evol. 143 (2), 2010
RESULTS
Alignment and phylogenetic analyses
The number of samples and statistics for each partition and
the combined data set are summarized in table 2. The best-t
model for all partitions was the general time reversible (GTR)
with an alpha parameter for the shape of the gamma distribu-
tion to account for among-site rate heterogeneity (GTR+G).
The only exception was the ITS region, in which a proportion
of invariable sites was added (GTR+G+I). The MP and ML
single-gene phylogenies provided different levels of resolu-
tion, but no differences with a bootstrap support greater than
75% were identied when compared, so we combined them
in a total evidence approach. Statistics (number of most par-
simonious trees; tree length; and consistency and retention
indices) for each analysis are reported in table 1.
For the combined analyses under the MP criterion, nine
of the ten independent PAUPrat searches converged on a best
score of 11526 steps and produced a total of 949 most parsi-
monious trees, which were used to compile a strict consensus
(not shown); this consensus tree comprised several polyto-
mies, especially near the tips. Under the ML criterion, the
best-t model for the combined matrix was GTR+G+I. This
model was used to perform the single ML run search (log
likelihood = − 79995.7), followed by rapid bootstrap analy-
ses.
When compared, analyses compiled under the MP and
ML criteria yielded very similar topologies. Moreover, as no
moderately to strongly supported differences were observed
between the two phylogenetic trees, only the ML topology
will be presented and discussed hereafter (gs 1 & 2).
Phylogenetic relationships
With the addition of the ninety ingroup samples used in the
present analysis, including representatives of several genera
of Sapindaceae s. lat. that had not previously been sequenced,
the phylogenetic relationships revealed here are highly con-
gruent with the informal system proposed by Buerki et al.
(2009). Based on sampling that includes at least one repre-
sentative of all genera traditionally placed in Sapindaceae
tribe Harpullieae, Aceraceae and Hippocastanaceae, our re-
sults further conrm that Xanthoceras sorbifolium Bunge
(previously assigned to Harpullieae by Radlkofer, 1933) is
resolved as sister to the remaining sampled members of Sa-
pindaceae s. lat. (however with a low BS; g. 1A). Our re-
sults also indicate that the other genera of Harpullieae belong
to three additional clades, one in subfam. Dodo naeoideae
and two in subfam. Sapindoideae (gs 1 & 2), conrming
the polyphyly of the tribe. Within Dodonaeoideae, ve of
the genera currently assigned to Harpullieae belong to the
Dodonaea group, viz. Arfeuillea, Eurycorymbus, Harpullia,
Magonia and Majidea (g. 1C), and Harpullia itself appears
to be polyphyletic, with the three species sampled occupying
very different positions within the phylogeny (expanded sam-
pling to include additional members of the genus are, howev-
er, needed to conrm this nding). Within Sapindoideae, two
of the three remaining genera assigned to Harpullieae (De-
lavaya and Ungnadia) are placed in the Dela vaya group, the
basal most lineage within the subfamily, and the third genus
(Conchopetalum) belongs to the Macphersonia group (g. 2).
The inclusion of Billia and Handeliodendron in our
analysis, along with additional species of Acer and Aesculus,
strengthens support for the monophyly of both Aceraceae and
Hippocastanaceae and conrms their sister relationship (g.
1A & B). Our results suggest the possible paraphyly of Acer
(with respect to Dipteronia) and of Aesculus (with respect to
Billia and Handeliodendron), although this nding should be
tested further with additional sampling. Support for the clade
comprising Sapindaceae s. str. (i.e. Dodonaeoideae plus Sa-
pindoideae) is likewise stronger in the present analysis (BS
= 88) than in that of Buerki et al. (2009; BS = 69; g. 1).
Moreover, Diplokeleba N.E.Br., long regarded as a member
of Sapindoideae (tribe Cupanieae), is instead placed within
Dodonaeoideae (g. 1C).
DISCUSSION
Polyphyly of Harpullieae
The results presented above clearly show that the tribe Har-
pullieae (as well as all other sapindaceous tribes with the
exception of Paullinieae), as dened initially by Radlkofer
(1890, 1933) and modied by Müller & Leenhouts (1976),
is highly polyphyletic, with members placed in no fewer than
four clades scattered among various parts of Sapindaceae
s. lat. Harrington et al. (2005) and Buerki et al. (2009) ar-
gued that additional sampling (especially of Harpullieae)
was required before taking a denitive stand regarding the
phylogenetic and taxonomic status of Xanthoceras. Although
we have now analyzed more than 70% of the genera and in-
cluded all those that are putatively related to Xanthoceras,
its precise phylogenetic position within Sapindaceae is not
strongly supported (BS < 50; g. 1A). However, both the MP
and ML analyses presented here clearly point toward Xan-
thoceras comprising a basal lineage with Sapindaceae s. lat.
(g. 1A). Moreover, a study comparing the performance of
supertree methods based on an identical dataset (Buerki et
al. in press) produced the same result, with both the Matrix
Representation with Parsimony and MinFlip supertree meth-
ods placing Xanthoceras as the most basally branching line-
age. This phylogenetic pattern might be explained either by
a higher rate of extinction in the lineage that now comprises
only Xanthoceras than in the other lineages, or alternatively
by a rapid diversication or radiation of these other lineages
resulting in a loss of phylogenetic signal (Judd & Olmstead
2004). In the case of Sapindaceae s. lat., the former hypoth-
esis seems more likely based on preliminary divergence time
estimations that place the origin of the clade in the Late Cre-
taceous (c. 110 My), with divergence among the four lineages
occurring between 90 and 80 My (Buerki et al. in prep.).
The pattern observed here, in which resolution between
lineages remains problematic even after sequencing a large
number of markers from a broad sampling of taxa, has been
observed in many other angiosperm groups, especially among
the rosids (Bello et al. 2009 and references within), such as
Fabales, where the relationships among the currently accept-
ed families remain unsolved. In order to clarify the situation
within Sapindaceae s. lat. and provide a practical classica-

Frequently asked questions

Q1. What contributions have the authors mentioned in the paper "Phylogeny and circumscription of sapindaceae revisited: molecular sequence data, morphology and biogeography support recognition of a new family, xanthoceraceae" ?

Lowry et al. this paper presented a survey of the state-of-the-art botanical research at the University of Neuchâtel in Switzerland. 

Q2. What was the procedure used to perform ML analyses?

ML analyses were performed using RAxML v. 7.0.0 (Stamatakis 2006, Stamatakis et al. 2008) with 1000 rapid bootstrap analyses followed by a search for the best-scoring tree in one single run. 

Q3. What is the phylogenetic pattern of Sapindaceae?

The tropical Chinese genus Delavaya, traditionally assigned to Harpullieae, has been viewed by several authors (e.g. Müller & Leenhouts 1976, Cronquist 1988) as a “link” between Sapindaceae and Hippocastanaceae through the temperate genus Handeliodendron. 

Q4. What is the significance of the inclusion of Billia and Handeliodendron in our?

The inclusion of Billia and Handeliodendron in their analysis, along with additional species of Acer and Aesculus, strengthens support for the monophyly of both Aceraceae and Hippocastanaceae and confirms their sister relationship (fig. 1A & B). 

Q5. Why did they not include a dozen monophyletic groups in their study?

Although they sketched an informal system that recognizes a dozen monophyletic groups, they did not propose new tribal limits within the four subfamilies as many potentially important genera of Sapindaceae were not included in their study due to the lack of sequenceable material. 

Q6. What is the phylogenetic pattern of Sapindaceae s.?

This phylogenetic pattern might be explained either by a higher rate of extinction in the lineage that now comprises only Xanthoceras than in the other lineages, or alternatively by a rapid diversification or radiation of these other lineages resulting in a loss of phylogenetic signal (Judd & Olmstead 2004). 

Q7. What was the procedure used to assess support at each node?

To assess support at each node, non parametric bootstrap analyses (Felsenstein 1985) were performedusing PAUP* (Swofford 2002) following the same procedure as in Buerki et al. (2009). 

Q8. How many samples were used in the present analysis?

With the addition of the ninety ingroup samples used in the present analysis, including representatives of several genera of Sapindaceae s. lat. 

Q9. What is the way to reduce the family assignment of Acer and Aesculus?

treating Sapindaceae broadly reduces these easily identified and widely recognized families to synonymy, changing the long-established family assignment of several well known, emblematic and widely cultivated genera, most notably Acer and Aesculus.