Multivariate morphometric analysis of Petrorhagia
subsect. Saxifragae (Caryophyllaceae) in Greece, with a
new species from SE Peloponnisos: P. laconica
Authors: Trigas, Panayiotis, Kougioumoutzis, Konstantinos, Ermidou,
Aikaterini, and Kalpoutzakis, Eleftherios
Source: Willdenowia, 48(1) : 137-146
Published By: Botanic Garden and Botanical Museum Berlin (BGBM)
URL: https://doi.org/10.3372/wi.48.48110
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Willdenowia
Annals of the Botanic Garden and Botanical Museum Berlin
PANAYIOTIS TRIGAS1*, KONSTANTINOS KOUGIOUMOUTZIS1, AIKATERINI ERMIDOU1 & ELEFTHERIOS
KALPOUTZAKIS2
Multivariate morphometric analysis of Petrorhagia subsect. Saxifragae (Caryophyllaceae) in Greece, with a new species from SE Peloponnisos: P. laconica
Version of record first published online on 5 April 2018 ahead of inclusion in April 2018 issue.
Abstract: The intra-generic relationships within the intriguing genus Petrorhagia are currently debated, as the genus
is underrepresented in recent taxonomic studies. In this study, we investigate the relationships among the species
of Petrorhagia [sect. Petrorhagia] subsect. Saxifragae occurring in Greece. Based on a combination of ordination
methods and discriminant analyses of 36 macromorphological characters, five species are recognized in Greece.
The analyses showed that all currently known species from Greece (P. fasciculata, P. graminea, P. phthiotica and P.
saxifraga) represent distinct taxonomic entities. According to our results, two recently collected populations from SE
Peloponnisos represent a fifth, new Petrorhagia species, which is first described and illustrated here as P. laconica.
It is related to the widespread P. saxifraga and the Greek endemic P. graminea, but clearly distinct from both species by a combination of morphological characters, including indumentum, inflorescence, calyx, capsule and seed
characters.
Key words: Caryophyllaceae, Greece, morphology, multivariate morphometric analysis, new species, Peloponnisos,
Petrorhagia, Petrorhagia subsect. Saxifragae, taxonomy
Article history: Received 18 December 2017; peer-review completed 7 February 2018; received in revised form 14
February 2018; accepted for publication 20 February 2018.
Citation: Trigas P., Kougioumoutzis K., Ermidou A. & Kalpoutzakis E. 2018: Multivariate morphometric analysis of
Petrorhagia subsect. Saxifragae (Caryophyllaceae) in Greece, with a new species from SE Peloponnisos: P. laconica.
– Willdenowia 48: 137 – 146. doi: https://doi.org/10.3372/wi.48.48110
Introduction
Caryophyllaceae include approximately 3000 species,
distributed in about 100 genera (Hernández-Ledesma &
al. 2015). The family has a primarily N-temperate distribution with a diversity centre in the E Mediterranean
and Irano-Turanian regions, while presence in the tropics
and the S hemisphere is limited and mostly confined to
higher elevations (Bittrich 1993; Greenberg & Donoghue
2011; Rabeler & Hartman 2005; Hernández-Ledesma &
al. 2015). The phylogenetic relationships within Caryophyllaceae is a field of active research (Fior & al. 2006;
Harbaugh & al. 2010; Greenberg & Donoghue 2011;
Hernández-Ledesma & al. 2015, etc.) and genera delimitation has been altered in some cases, reflecting the
results of recent molecular studies (e.g. Dillenberger &
Kadereit 2014).
Petrorhagia (Ser.) Link (Caryophylloideae, Caryophylleae) is a small genus of c. 33 species, distributed
in the Mediterranean area, Europe and W Asia (from the
Canary Islands east to Kashmir), with a diversity centre
in Greece and Turkey (Ball & Heywood 1964; Georgiou
1997). In the past, it was placed in different genera such
as Dianthus L., Gypsophila L., Kohlrauschia Kunth and
Tunica Scop. Evidence from both traditional and phylogenetic systematics support its recognition as a distinct
1 Laboratory of Systematic Botany, Department of Crop Science, Agricultural University of Athens, Iera Odos 75, 118 55, Athens,
Greece; *e-mail: trigas@aua.gr (author for correspondence).
2 Division of Pharmacognosy and Chemistry of Natural Products, School of Pharmacy, National and Kapodistrian University of
Athens, 157 71 Athens, Greece.
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138
Trigas & al.: Petrorhagia subsect. Saxifragae in Greece, with P. laconica from SE Peloponnisos
taxon at the genus rank, which clusters as sister to a clade
including Dianthus and Velezia L. (Ball & Heywood
1964; Harbaugh & al. 2010; Greenberg & Donoghue
2011; Pirani & al. 2014; Hernández-Ledesma & al. 2015;
Hilooğlu & al. 2016).
Recent data on the infrageneric classification of
Petrorhagia is still scarce, as the genus is rather poorly
sampled. The available data (Greenberg & Donoghue
2011; Hilooğlu & al. 2016) are fragmentary and do not
allow a reliable infrageneric classification. As a result,
most recent treatments of the genus follow the monograph of Ball & Heywood (1964) that recognizes five
sections within Petrorhagia, distinguished by petal and
seed characters, life-cycle, leaf venation and the presence/absence of epicalyx bracts. Out of the five sections,
P. sect. Petrorhagia includes ten species (seven of them
occurring in Greece and five endemic to the country) distributed in two subsections: P. subsect. Saxifragae Ball
& Heywood and P. subsect. Thessalae Ball & Heywood.
The two subsections are distinguished by stem branching (much branched vs simple or with few branches),
inflorescence (flowers solitary or fasciculate vs capitate)
and bract (lanceolate or ovate, membranous, 1-veined vs
broadly ovate or suborbicular, membranous and 1-veined
or brown-scarious and many-veined) morphological
characters.
In May 2014, during field work in SE Peloponnisos,
we detected a population of an interesting Petrorhagia
species, growing on coastal sand-dunes, an unusual habitat for the members of the genus. Careful examination
of the collected specimens revealed that plants from SE
Peloponnisos belong to P. sect. Petrorhagia, and they resemble P. saxifraga (L.) Link, a widely distributed species in C and S Europe and SW Asia. After a detailed
morphological study, it became apparent that plants from
SE Peloponnisos are clearly distinct from P. saxifraga,
as well as from all known Petrorhagia species and they
belong to a new, undescribed species. Dr E. Kalpoutzakis
had also found the same species in May 2013 in another
locality of SE Peloponnisos.
The morphological characters of the new species
from SE Peloponnisos, described here as Petrorhagia
laconica, support its classification in P. subsect. Saxifragae. Species delimitation within P. subsect. Saxifragae has never been studied in detail. All species of
P. subsect. Saxifragae, except P. riphaea (Pau & Font
Quer) Ball & Heywood that is the only species of this
group distributed in Africa (Morocco), are distributed
in Greece. Thus, the scope of this study is manifold; it
aims to resolve the apparent ambiguities within P. subsect. Saxifragae and to evaluate the taxonomic validity
of the two recently discovered deviating Petrorhagia
populations. More specifically, we aim: (1) to clarify the
patterns of morphological variation within P. subsect.
Saxifragae in Greece, (2) to disclose the level of morphological differentiation for recognized species, (3) to
indicate the most informative characters for the iden-
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tification of the species, and (4) to describe the newly
discovered species.
Material and methods
Plant material
Data for the multivariate analyses were recorded from
herbarium specimens deposited in UPA and ATH (acronyms follow Thiers 2017+) belonging to Petrorhagia
fasciculata (Margot & Reut.) P. W. Ball & Heywood, P.
graminea (Sm.) P. W. Ball & Heywood, P. phthiotica
(Boiss. & Heldr.) P. W. Ball & Heywood and P. saxifraga. We collected several specimens of P. laconica in
the field. All specimens included in the analyses were
selected so as to represent the entire distribution range
of the taxa in Greece, as well as the morphological variation in each species. Only well-preserved and intact
specimens were considered in the analyses. The total
number of herbarium specimens included in the analyses was 97. A list of the examined specimens is provided in Table S1 (see Supplementary Material online).
Each specimen was preliminary identified as one of the
five aforementioned species. Species identification and
nomenclature are according to Ball & Heywood (1964),
Georgiou (1997) and Dimopoulos & al. (2013).
Characters recorded
Twenty-seven quantitative and 9 qualitative (binary)
morphological characters were scored for the herbarium
specimens included in our analyses (Table 1). The selected characters represent those previously quoted as diagnostic and are the ones most commonly used in the latest comprehensive monographs, regional and local floras
(Ball & Heywood 1964; Coode & Cullen 1967; Georgiou
1997). Capsule and seed morphological characters, although with a diagnostic value in the genus Petrorhagia
(Ball & Heywood 1964), were excluded from the morphometric analyses as most studied specimens were in
flower, lacking capsules and seeds. These characters,
however, were used for the documentation of morphological differences among P. laconica and its closest relatives. All the characters in the herbarium specimens were
measured under a stereomicroscope using a ruler with
the precision of 0.5 mm.
Morphometric analyses
Basic statistical parameters (mean, minimum and maximum value, standard deviation, 5th and 95th percentiles)
were calculated for each species included in the analyses.
We used a combination of ordination methods and discriminant analyses in the morphometric analyses of the
specimens (Marhold 2011).
We first tested whether any character deviated from
a normal distribution using the Shapiro-Wilk statistic
Willdenowia 48 – 2018
139
Table 1. Characters used in the morphometric analyses.
Character
abbreviation
Detailed character definition
a1
a2
a3
a4
a5
a6
a7
a8
a9
a10
a11
a12
a13
a14
a15
a16
a17
a18
a19
a20
a21
a22
a23
a24
a25
a26
a27
a28
a29
a30
a31
a32
a33
a34
a35
a36
Number of flowering stems
Length of flowering stems (cm)
Length of the unbranched part of flowering stem (cm)
Length of the inflorescence (cm)
Glandular hairs present at the lower 1/3 of the stem
Glandular hairs present at the middle 1/3 of the stem
Glandular hairs present at the upper 1/3 of the stem
Eglandular hairs present at the lower 1/3 of the stem
Eglandular hairs present at the middle 1/3 of the stem
Eglandular hairs present at the upper 1/3 of the stem
Number of flowers per flowering stem
Number of lateral branches per flowering stem
Length of lateral branches per flowering stem (cm)
Number of flowers per lateral branch
Number of flowers per terminal unit of the inflorescence
Length of lower leaves (mm)
Width of lower leaves (mm)
Length of middle leaves (mm)
Width of middle leaves (mm)
Length of internodes at the middle of the stem (mm)
Number of leaves at the middle of the stem
Ratio of leaves/internodes length at the middle of the stem
Number of veins on leaves
Length of petals (mm)
Width of petals (mm)
Length of calyx (mm)
Length of calyx teeth (mm)
Width of calyx teeth at their base (mm)
Length of pedicels (mm)
Bract length (mm)
Ratio pedicel length/calyx length
Ratio petal length/calyx length
Number of veins on sepals
Glandular hairs present on calyx
Eglandular hairs present on calyx
Epicalyx bracts present
and we log10-transformed any characters that deviated
from normality. Then, we computed the correlation coefficients between each character pair in order to reveal
highly correlated characters and to ensure that no high
correlations (> 0.95 – Španiel & al. 2017) were present
that could potentially distort the discriminant analysis.
As a second step, we performed several stepwise canonical and classificatory Discriminant Analyses (DAs)
in order to: (1) identify the variables having the highest potential as diagnostic characters and (2) test the
effectiveness of the discrimination rules by using the
Leave-One-Out cross-validation (LOO). The value of
the inclusion and the exclusion criterion in the stepwise
DAs was set at F = 0.05 and F = 0.1, respectively. Wilk’s
lambda was used to assess the significance of each variable and Discriminant Function (DF). The Maximum
Chance Criterion (MCC) and the Proportional Chance
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Criterion (PCC) were used to determine whether
the prediction equation was better than random
chance (Huberty & Olejnik 2006). The DAs were
checked for outliers. Finally, we examined the
morphological variation in our dataset in relation
to the species boundaries by analysing the ranges
of the characters using core functions in the R
computing environment (R Core Team 2015). All
the analyses were carried out using IBM SPSS 24.
The correlation coefficients were calculated with
the “usdm” (Naimi & al. 2014) package, while the
stepwise discriminant analysis plots were visualized via the ggplot2 (Wickham, 2009) package in
the R computing environment. The Maximum and
Proportional Chance criteria were ran under the
Zclass algorithm kindly provided by John D. Morris (Florida Atlantic University).
Results
Characters scored
The basic statistical parameters for all species
are given in Table S2. The only character that
had a correlation coefficient above the threshold
was a10 (eglandular hairs present at the upper ⅓
of the stem) and was thus excluded from further
analyses.
Multivariate analyses
The DA clearly discriminated the five Petrorhagia
species. Sixteen of the characters emerged as statistically significant (Table 2), with LOO showing
a 100 % correct classification, being significantly
better than random chance for both the PCC and
MCC (P < 0.001, Table S3). These characters
showed no to little overlap across the five species (Fig. 1). The first (DF1), the second (DF2),
the third (DF3) and the fourth (DF4) discriminant
function explained 86.6 %, 11.5 %, 1.3 % and 0.6 %
of the total variation, respectively (Table 2, Fig. S1).
Among the morphological characters used, the presence
and the type of the indumentums are the most informative characters for species distinction in P. subsect.
Saxifragae. The highest discriminative function (DF1)
is primarily influenced by the presence of eglandular
hairs at the middle part of the stem (a9). The presence
of glandular hairs on calyx (a34) and eglandular hairs
at the lower part of the stem (a8) have also high discriminant validity in DF1 (Table 2). The presence of
eglandular hairs on calyx (a35) and glandular hairs at
the middle/upper part of the stem (a6/a7) are the characters loading most heavily on DF2 and DF3, respectively
(Table 2). The five Petrorhagia species included in the
analyses are clearly distinct from one another (Table S3,
Fig. 1, S1, S2).
140
Trigas & al.: Petrorhagia subsect. Saxifragae in Greece, with P. laconica from SE Peloponnisos
Fig. 1. Stepwise discriminant analysis plot for the five Petrorhagia species. The squares indicate the function group centroid of
each species.
Discussion
Multivariate morphometrics provide a powerful mean
in order to assess the variation patterns at various taxonomic levels and is especially useful in disentangling the
boundaries between closely related and/or poorly differentiated taxa (e.g., Kougioumoutzis & al. 2015), as well
as in unveiling the most informative and discriminating
characters that differentiate among them (Marhold 2011).
In the present study, the application of multivariate morphometrics resulted in important conclusions with taxonomic consequences. More specifically, the results of
morphometric analyses enabled the delimitation of five
well-separated species and the elucidation of the identity
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of the deviating Petrorhagia populations from SE Peloponnese: the latter constitute a new, distinct and rather
rare taxon, herein described as P. laconica.
Petrorhagia subsect. Saxifragae is a taxonomically
complicated group with several overlapping characters.
Our morphometric analyses, however, showed that all
species are clearly distinguished from each other. Their
distinction can be achieved even without using morphological seed characters, an important diagnostic feature
in the genus Petrorhagia. The latter were not included in
the morphometric analyses, as most specimens used were
not in fruit.
The presence and type of hairs on stem and calyx have
emerged as important diagnostic characters. The pres-
Willdenowia 48 – 2018
141
Table 2. Stepwise discriminant analysis results for the five Petrorhagia species
included in the present study based on 14 morphological characters, as well as
the eigenvalues of the discriminant functions and the proportion of variance (PV)
explained by each discriminant function. DF1, DF2, DF3 and DF4 indicate the
first, the second, the third and the fourth discriminant function, respectively. F, T
and WD indicate the F-test P values, the tolerance values, as well as the Wilk’s
lambda values of the discriminant functions and characters retained in the stepwise
discriminant analysis, respectively. SML indicates the loadings from the stepwise
discriminant analysis (i.e. the correlation of the characters with the discriminant
functions). Character abbreviations follow Table 1. Higher values are shown in
bold.
Character
T
F
WD
DF1
DF2
DF3
DF4
Eigenvalue
–
–
–
205.23
27.22
3.12
1.38
PV
–
–
–
86.6
11.5
1.3
0.6
WD
–
–
–
0.00
0.00
0.10
0.42
0.85
0.01
0.00
0.35
-0.06
0.11
a34
0.42
0.00
0.00
0.26
0.06
0.07
0.16
a15
0.58
0.00
0.00
-0.06
0.22
0.03
0.09
a35
a31
0.51
0.09
0.00
0.00
0.00
0.00
-0.06
0.06
0.23
-0.03
0.69
-0.36
-0.23
0.02
a8
0.45
0.00
0.00
0.20
0.03
0.34
0.32
SML
a9
0.09
a29
0.08
0.00
0.00
-0.09
-0.13
-0.29
0.03
a28
0.67
0.01
0.00
-0.06
-0.16
0.25
-0.14
a25
0.60
0.03
0.00
-0.07
-0.15
0.24
-0.02
a7
0.28
0.00
0.00
-0.05
0.18
-0.19
0.53
a6
0.16
0.00
0.00
-0.05
0.18
-0.19
0.53
a5
0.24
0.00
0.00
-0.09
0.38
-0.21
0.44
a14
0.38
0.00
0.00
-0.13
0.00
-0.08
0.37
a4
0.69
0.03
0.00
-0.15
0.00
0.02
0.28
a27
0.23
0.00
0.00
-0.05
-0.04
0.11
-0.26
a30
0.60
0.03
0.00
0.03
0.03
-0.04
-0.11
ence of eglandular hairy stems throughout their length is
a unique feature of Petrorhagia laconica. Petrorhagia fasciculata and P. phthiotica are the only species with an indumentum of glandular hairs on stems, while the stems of
P. graminea are covered by a mixture of glandular and eglandular hairs, at least at base. All examined specimens of
P. saxifraga had glabrous stems. Furthermore, P. laconica
is the only species with a glandular hairy calyx. The calyx of P. graminea is predominantly covered by eglandular
hairs, often mixed with few glandular hairs. All examined
specimens of P. fasciculata had eglandular hairy calyces,
while all calyces in P. phthiotica and P. saxifraga were glabrous.
Length of the inflorescence, number of lateral branches and flowers per flowering stem, width of lower leaves
and the ratio pedicel/calyx length further differentiate
Petrorhagia laconica from all other species of P. sect.
Saxifragae (Table S2, Fig. S1). Moreover, P. laconica, together with P. saxifraga, are the only species with calyces
enclosed by epicalyx bracts; in the specimens of all other
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species (including P. fasciculata) there
are no bracts enclosing the calyx. The
small petals and the large number of
flowers per terminal inflorescence unit
easily distinguish P. fasciculata from
all other species. Petrorhagia graminea
and P. saxifraga are the only species
with 3-veined sepals and they also have
the largest petals. The 3-veined leaves
and the short stems further differentiate
P. phthiotica from all other members of
P. sect. Saxifragae.
The results of our analyses have
revealed a diagnostic character not previously used in the genus Petrorhagia.
Although the length of leaves is similar
in all species examined, leaf width varies among species. Petrorhagia laconica and P. saxifraga have narrow basal
leaves compared to the other species.
Furthermore, cauline leaves are diminishing in size toward the apex in all
species, but diminishing in leaf length
only, while leaf width remains stable,
has been observed only in P. laconica
(Table S2, Fig. S1).
Taxonomy
Petrorhagia laconica Trigas, Kalpoutz.
& Kougioum., sp. nov. – Fig. 2.
Holotype: Greece, Peloponnisos, sand
dunes c. 3.5 km NW of Neapoli village, 36°31.721'N, 23°01.273'E, 2 m,
22 May 2017, Trigas 6311 (ACA; isotypes: B, UPA).
Diagnosis — Related to Petrorhagia saxifraga, from
which it differs in the following morphological characters:
underground stock rooting at nodes; stems procumbent
to ascending or erect, glaucous-green, simple or rarely
with few (1 – 3[ – 6]) lateral branches at upper ⅓, minutely
papillose-scabridulous except glabrous at 1 – 4 upper internodes; leaves closely appressed to stem, rigid; flowers solitary or rarely paired, 1(or 2) per flowering stem,
rarely up to 6; calyx minutely glandular pubescent; ribs
purplish brown, obscurely 1-veined; capsule 2.5 – 3 mm
long, sparsely tuberculate at proximal ½; seeds with flat,
non-thickened margin.
Description — Plants perennial, with branched, slender,
woody underground stock rooting at nodes, producing few
to several flowering stems. Flowering stems procumbent
to ascending or erect, glaucous-green to purplish brown,
7 – 40 cm long, simple or rarely with few (1 – 3[ – 6]) lateral
branches at upper ⅓, minutely papillose-scabridulous ex-
142
Trigas & al.: Petrorhagia subsect. Saxifragae in Greece, with P. laconica from SE Peloponnisos
Fig. 2. Petrorhagia laconica – A: sand-dune habitat NW of Neapoli village in SE Peloponnisos with evergreen shrubs (locus classicus), 22 May 2017; B: individual with simple, procumbent-ascending stems at the locus classicus, 16 May 2014; C: middle part
of stem with leaves; D: upper part of stem with flower; E: flower, lateral view; F: flower, apical view; G: immature capsule; H: seed,
dorsal face; I: seed, ventral face. – Scale bars: C – F: 3 mm; G: 1 mm; H, I: 500 μm. – All photographs by Panayiotis Trigas except
G by Eleftherios Kalpoutzakis.
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Willdenowia 48 – 2018
cept glabrous at 1 – 4 upper internodes; internodes markedly unequal, larger at middle of stem, diminishing in
size toward base and apex. Leaves linear-subulate, ⅓ – 1¼
as long as internodes, rigid, 1-veined, united at base into
a sheath 1 – 1.5 mm long, with a purplish brown ring at
base, apex acuminate to caudate; lower leaves 7 – 19 ×
0.5 – 1 mm, minutely roughly papillose at margin, otherwise glabrous; cauline leaves closely appressed to stem,
3 – 16 × 0.5 – 1 mm, glabrous. Flowers solitary or rarely
paired at apices of stems and branchlets, 1(or 2) per flowering stem, rarely up to 6, subtended by 4 straw-coloured,
lanceolate, hyaline, glabrous epicalyx bracts, sometimes
purplish-tinged at midrib. Calyx cylindric, 3 – 6 mm long,
minutely glandular pubescent; ribs purplish brown, obscurely 1-veined; teeth oblong-triangular, 0.5 – 1 mm
long, apex obtuse. Petals white, 4 – 8 × 1.5 – 3 mm, abaxial
surface purple-veined, adaxial surface with three longitudinal purplish stripes at base, with glabrous claw not
distinctly delimited from emarginate lamina. Anthers
white. Ovary oblong-ovoid, c. 1 mm long; anthophore
green, c. 0.5 mm long, glabrous. Capsule pale brown,
ovoid, 2.5 – 3 mm long, smooth or sparsely tuberculate at
proximal ½. Seeds blackish brown, ovate-oblong, 1 – 1.2
× 0.7 – 0.8 mm, both surfaces reticulate, margin flat, not
thickened, apex long mucronate.
Distribution — Petrorhagia laconica is distributed in the
Malea Peninsula in SE Peloponnisos. Two populations
have been discovered so far; the first one is located at the
Gulf of Neapoli, right across Elafonisos Island, while the
second one was found close to Sykea village, c. 25 km
N-NW of the first population. It is the southernmost distributed species of P. subsect. Saxifragae in Europe.
Ecology — Petrorhagia laconica is known to grow in
two different habitats. In Neapoli, all individuals were
observed to grow in the inner sand dune zone, usually
surrounded by sclerophyllous shrubs, such as Anthyllis hermanniae L., Ceratonia siliqua L., Pistacia lentiscus L., Pyrus spinosa Forssk. and Smilax aspera L.
Petrorhagia laconica grows in stabilized sand dunes
among the shrubs, together with other sand dune adapted
taxa, such as Anthemis tomentosa L., Asphodelus ramosus L., Centaurea sonchifolia L., Elytrigia juncea (L.)
Nevski, Linaria tenuis (Viv.) Spreng. and Scirpoides
holoschoenus (L.) Soják.
Close to Sykea village, Petrorhagia laconica grows
in small remnant patches of macchie and phrygana
formations that form a mosaic among the abundant olive groves. The population occupies a small area at
120 – 140 m a.s.l., on flysch. Shrub species composition
of macchie is similar to that of the locus classicus, with
Lavandula stoechas L., Olea europaea L., Phlomis fruticosa L., Pistacia lentiscus and Pyrus spinosa the predominant species. Petrorhagia laconica usually grows in
small patches among the shrubs, together with Ballota
acetabulosa (L.) Benth., Cistus salviifolius L., Globular-
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143
ia alypum L., Hypericum triquetrifolium Turra, Sarcopoterium spinosum (L.) Spach, Silene nocturna L., etc.
Conservation status — In Neapoli Lakonias,
Petrorhagia laconica grows on a large sandy beach
c. 3.5 km long, between Neapoli and Viglafia village.
The width of sand dunes along this beach ranges from
30 to 150 m, and the species is exclusively confined to
the inner sand dune zone, where it is fairly rare. It usually forms small groups of 5 – 30 individuals, but single
remote plants were also observed. The total population
of Neapoli is estimated to include 300 – 400 individuals, mainly concentrated at the E part of the beach. The
Sykea population counts c. 500 individuals distributed
in an area of c. 0.1 km2.
Habitat loss and touristic development are the main
threats that Petrorhagia laconica faces at its locus classicus. Sand dunes have been partly turned into cultivated
fields at the E half of the beach, almost certainly leading
to a significant population decline. The habitat also hosts
thousands of swimmers during summer, being an unpredictable risk factor for its long term survival. The whole
area, however, belongs to the Natura 2000 network of
protected areas (Periochi Neapolis kai Nisos Elafonisos,
GR2540002), and numerous human activities that could
create additional risks for the population of P. laconica in
Neapoli area are fortunately forbidden.
Habitat loss is also the main threat that Petrorhagia
laconica faces in Sykea area, as more than 50% of the
area previously covered with natural vegetation have
been turned into cultivated fields. As a result, it is irrefutable that the species has suffered a severe population decline in the near past, which can be estimated as probably
approaching the percentage of habitat loss.
The flora of SE Peloponnisos has been intensively explored during the last decades (e.g. Kalpoutzakis & Constantinidis 2005, 2006; Greuter 2012; Kalpoutzakis &
al. 2012). The recent discovery of Petrorhagia laconica
indicates that the species should not be common in this
area. The habitat types in which it grows (especially the
mosaic with macchie and phrygana formations), however, are abundant in SE Peloponnisos. Consequently,
the existence of additional populations of this tiny and
easily overlooked species cannot be ruled out. The extent
of occurrence (EOO) does not exceed 25 km2 and since
P. laconica is a very local species, its area of occupancy
(AOO) is much smaller, apparently less than 1 km2. Ergo,
due to: (1) the restricted EOO and AOO, (2) the current
existence of max. 900 mature individuals distributed in
two populations and (3) the high possibility that the extant localities and populations could be eradicated as a
result of human interference, P. laconica is assigned to
the Endangered (EN) IUCN (2001) category, following
criteria B1ab(i,ii,iii,iv)+2ab(i,ii,iii,iv). Petrorhagia laconica should be carefully monitored, cultivated ex situ
in botanical gardens and special conservation measures
be taken to safeguard its populations.
144
Trigas & al.: Petrorhagia subsect. Saxifragae in Greece, with P. laconica from SE Peloponnisos
Table 3. Main morphological differences among Petrorhagia laconica, P. saxifraga and P. graminea.
P. laconica
P. saxifraga
P. graminea
rooting at nodes
not rooting at nodes
not rooting at nodes
Stems
procumbent to ascending or erect,
glaucous-green, simple or rarely
with few (1 – 3[– 6]) lateral branches
at upper ⅓, minutely papillosescabridulous except glabrous at
1 – 4 upper internodes
arcuately ascending to erect, green,
usually branched to much-branched,
glabrous to shortly papillose or
scabrid-pubescent at least in
lower part
ascending to erect, green, sparingly
branched, glabrous to densely
pubescent
Leaves
closely appressed to stem, linearsubulate, rigid
± spreading, linear to linearlanceolate, herbaceous
± spreading, linear, herbaceous
Inflorescence
flowers solitary or rarely paired,
1(or 2) per flowering stem,
rarely up to 6
flowers solitary or in fascicles,
2 – 59 per flowering stem
flowers solitary or in fascicles of
2 or 3, 2 – 37 per flowering stem
present
present
absent
Calyx
minutely glandular pubescent; ribs
purplish brown, obscurely 1-veined
glabrous or occasionally sparsely
eglandular pubescent; ribs green,
3-veined
densely eglandular pubescent to
glabrous; ribs green, 3-veined
Capsule
2.5 – 3 mm long, smooth or sparsely
tuberculate at proximal ½
3.5 – 5 mm long, smooth
3 – 5 mm long, smooth
Seeds
ovate-oblong, 1 – 1.2 × 0.7 – 0.8 mm,
margin flat, not thickened
ovate, 0.9 – 1.6 × 0.6 – 1.1 mm,
margin curved, thickened
oblong to suborbicular, 0.8 – 1.5 ×
0.7 – 1 mm, margin ± curved,
slightly thickened
May – August
May – August
September – January
Character
Underground stock
Epicalyx bracts
Flowering period
Etymology — The specific epithet refers to Laconia (Lakonia, also known as Lacedaemonia), a region that covers
almost the entire SE part of the Peloponnisos, where the
new species was collected. This name goes back to the
historical times, when Laconia was the principal region
of the Spartan state.
Taxonomic relationships — Petrorhagia laconica undoubtedly belongs to P. sect. Petrorhagia, as it is indicated by its 1-veined leaves, the presence of epicalyx bracts,
the not abruptly clawed petals, the reticulate, blackishbrown seeds and the perennial life-cycle. The thickened
seed margin is not a common feature of all species in P.
sect. Petrorhagia, as it is indicated by Ball & Heywood
(1964). Petrorhagia dianthoides (Sm.) P. W. Ball & Heywood, P. fasciculata, P. grandiflora Iatrou and P. thessala
(Boiss.) P. W. Ball & Heywood have a flat, thin seed margin, similar to that of P. laconica.
Within Petrorhagia sect. Petrorhagia, P. laconica
shows close affinities to the members of P. subsect. Saxifragae. The solitary or paired flowers and the lanceolate,
1-veined epicalyx bracts advocate for the inclusion of P.
laconica within P. subsect. Saxifragae. Flower and seed
morphological characters further support this taxonomic
view. The simple or sparingly branched stems, however,
resemble the members of P. subsect. Thessalae, which
otherwise have significant morphological differences from
P. laconica (e.g. capitate inflorescence, broadly ovate or
sub-orbicular bracts, larger and different petals, etc.).
Petrorhagia laconica appears to be one of the most
distinct species in P. sect. Petrorhagia. The results of
multivariate morphometric analyses (Tables 2, S3, Fig.
1, S1, S2) support its distinct taxonomic position with-
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in P. subsect. Saxifragae. The closest related species
seem to be P. saxifraga and P. graminea, which, however, show significant morphological differences from
P. laconica (see also Table 3). The possibility of vegetative reproduction (underground stolons connecting different individuals have been observed in the field) and
the tuberculate capsule have not been recorded in other
Greek Petrorhagia species, and they probably represent
unique features within the whole genus. The discovery
of P. laconica is in line with Trigas & al. (2007, 2012),
which state that SE Peloponnese is one of the important regions in Greece in terms of endemic plant species
richness and conservation, as well as a significant diversity centre for Petrorhagia, because more than 30 % of
the species diversity of the whole genus is hosted in this
small region.
Additional specimens examined — Greece: Peloponnisos, c. 3.5 km S-SE of Sykea village, 36°43.970'N,
22°57.079'E, 130 m, macchie and phrygana among olive
groves, on flysch, 6 May 2013, Kalpoutzakis 4294 (ACA);
ibid., 29 Jul 2017, Kalpoutzakis 4959 (ACA); c. 2.5 km
S-SE of Sykea village, 36°44.552'N, 22°57.209'E, 120 m,
macchie and phrygana among olive groves, on flysch, 22
May 2017, Trigas 6312 (ACA).
Acknowledgements
We would like to thank Prof. Emer. Arne Strid and an
anonymous reviewer for insightful comments that greatly
improved the manuscript. We are grateful to the curators
of UPA and ATH for loaning specimens for our study. We
Willdenowia 48 – 2018
also wish to thank Dr Aimilia-Eleni Nikolopoulou (Agricultural University of Athens) for collecting specimens
of Petrorhagia laconica with mature capsules.
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