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ANNALES · Ser. hist. nat. · 27 · 2017 · 1
original scientifi c article                 DOI 10.19233/ASHN.2017.02
received: 2017-02-16
DITTRICHIA GRAVEOLENS – HOW DOES SOIL SALINITY DETERMINE 
DISTRIBUTION, MORPHOLOGY, AND REPRODUCTIVE POTENTIAL?
Nina ŠAJNA 
Faculty of Natural Sciences and Mathematics University of Maribor, Koroška 160, Maribor, Slovenia
nina.sajna@um.si
Kristijan ADAMLJE
Faculty of Natural Sciences and Mathematics University of Maribor, Koroška 160, Maribor, Slovenia
Mitja KALIGARIČ
Faculty of Natural Sciences and Mathematics University of Maribor, Koroška 160, Maribor, Slovenia &
Faculty of Life Sciences, 2311 Pivola, Slovenia
ABSTRACT
Road salting in winter, which improves the safety of road travel, has a strong impact on species inhabiting road 
verges, since it creates habitats with increased salinity. Higher levels of soil salinity represent a habitat that can 
be occupied by plants exhibiting special adaptations and tolerance. As a result, Dittrichia graveolens, which is 
indigenous in the Mediterranean area, is moving inland and can be found in several Central European countries. We 
studied how soil salinity determines the D. graveolens plant height, reproductive potential and distribution along 
the road verge. Plant height was related to soil electrical conductivity (EC) – a measure for salinity. Our results show 
that the species grows best in soils where the EC ranges from 110 to 170 µS/cm, while at values less than 100 µS/
cm, no plants were observed. 
Key words: invasive species, road verges, road salting, Slovenia
DITTRICHIA GRAVEOLENS – COME LA SALINITÀ DEL SUOLO DETERMINA 
DISTRIBUZIONE, MORFOLOGIA E POTENZIALITÀ RIPRODUTTIVA DELLA SPECIE?
SINTESI
La salatura delle strade in inverno, che migliora la sicurezza dei viaggi, ha un forte impatto sulle specie che 
vivono sui bordi stradali, in quanto crea habitat con salinità elevata. I livelli più alti di salinità del suolo caratterizzano 
un habitat che può essere occupato da piante che presentano adattamenti e tolleranze speciali. Di conseguenza, 
Dittrichia graveolens, pianta indigena nell’area mediterranea, si sta muovendo verso l’interno e può essere trovata 
in diversi paesi dell’Europa centrale. Gli autori hanno studiato come la salinità del suolo determina l’altezza della 
pianta di D. graveolens, il potenziale riproduttivo e la distribuzione lungo il bordo stradale. L’altezza della pianta è 
legata alla conduttività elettrica del suolo (CE) – una misura per la salinità. I risultati mostrano che la specie cresce 
meglio su terreni in cui la CE varia da 110 a 170 µS/cm, mentre dove i valori sono inferiori a 100 µS/cm non sono 
state osservate piante.
Parole chiave: specie invasiva, bordi stradali, salatura delle strade, Slovenia
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INTRODUCTION
The introductions of the majority of naturalized alien 
plants to Europe has happened since 1750 (Williamson 
et al., 2009) and has resulted in the establishment of 
more than 3700 species, while the current invasion rate 
is estimated at 6.2 new species per year (Lambdon et 
al., 2008). These species belong to more than 200 plant 
families, among which Asteraceae, Poaceae, Rosaceae 
and Brassicaceae are predominant (Pyšek et al., 2009). 
These are large families with many species represen-
tatives known to be weeds. Approximately one half of 
naturalized alien plants in Europe are alien plants from 
another continent (e.g. North and South America, Asia), 
while the other half is represented by species from an-
other part of Europe, where the plants  are native. Many 
of common agricultural weeds invasive in Europe are 
also native to the Mediterranean (Pyšek et al., 2009).
There are numerous routes and vectors for alien 
species introduction; however, we focus here on high-
ways, which represent an opportunity for introduction 
into a new region and at the same time promote further 
dispersal with the help of vehicular transportation along 
road corridors (Pollnac et al., 2012 and references 
therein). In Central Europe several invasive species are 
known as “Autobahn-Pfl anzen”, among them Dittri-
chia graveolens (L.) Greuter (syn. Inula graveolens (L.) 
Desf.), Senecio inaequidens DC. and Atriplex micrantha 
Ledeb. – examples of alien plant species which are able 
to spread rapidly along roads (Heger & Böhmer, 2006). 
Even though highways are highly disturbed, stressful, 
and fragmenting structures in the human-dominated 
landscape, their maintenance results in the creation of 
road verges – often dry, sunny, nutrient-poor and grav-
el-like habitats, which are dominated by environmental 
conditions different from most natural habitats in their 
vicinity. Additionally, human activities can impact road 
verges in such way that they represent a new, artifi cial 
habitat, one not previously existing. They exhibit altered 
physical and chemical soil characteristics; for example, 
texture, compaction, water content, leakage of deicing 
chemicals causing salinity, nitrogen deposition and 
pollution (Thompson et al., 1986; Cale & Hobbs, 1991; 
Truscott et al., 2005). Additionally, they represent highly 
disturbed habitats for plants because of repeated distur-
bance from maintenance like mowing, shrub clearing 
or herbicide application (Gelbard & Belnap, 2003). The 
use of deicing chemicals has a profound impact on road 
verge habitats, since it can cause soil salinity and saline 
spray, directly impacting standing vegetation. Therefore, 
such habitats can be occupied by plants exhibiting 
special adaptations or tolerance, among which maritime 
species are particularly successful (Scott & Davison, 
1982). Invasions have been reported for Spergularia me-
dia and S. marina (Kocián, 2015b), Atriplex micrantha 
(Smettan, 2002), the grasses Puccinellia distans, P. ma-
ritima, P. fasciculata, Aster tripolium, Plantago maritima 
and P. coronopus (Scott & Davison, 1982) and many 
more.
Additionally, such habitats are less likely to be 
dominated by numerous native plants. The combination 
of a high variety of non-native seeds transported along 
roads and the presence of road verge habitats sparsely 
occupied by native species makes road verges into 
opportunity habitats for alien plants.
We were therefore interested in the occurrence of 
a plant of southern origin, annual species Dittrichia 
graveolens, which has been spreading along Slovenian 
highways. It is distributed across the central part of the 
country where there is a harsher climate, while it does 
not occur in the coastal region of Slovenia (Frajman & 
Kaligarič, 2009), where a closely related perennial, D. 
viscosa, can be found native to Istria (Wraber, 1999; 
Jogan et al., 2001). We hypothesized that D. graveolens 
is not a particularly good competitor, and therefore 
not present in the sub-Mediterranean region, while at 
the same time it is tolerant of higher concentrations of 
salinity, which enables its establishment further north 
because of winter road maintenance with deicers.
MATERIAL AND METHODS
Study species
Dittrichia graveolens is an annual herbaceous plant 
in the family Asteraceae. It reaches heights of 10 to 50 
cm (own observation). Leaves and stem, as well as the 
capitulum involucre are densely glandular and hairy. 
Yellow fl owers are female if lingulate and hermaph-
rodite if tubular (Brullo & de Marco, 2000). In Central 
Europe the fl owering occurs from September to October 
(Kocián, 2015a). Achenes are 1.8-2 mm long, with a 4 
mm pappus (Brullo & de Marco, 2000). It is native to the 
Mediterranean basin and partly to the Western Atlantic 
coast and the Middle East (Brullo & de Marco, 2000). It 
has invaded other European regions and regions of the 
world with similar climates, including California, Aus-
tralia and New Zealand (Preston, 2006). In Slovenia it 
was fi rst observed in 2008 along Highways A1 from Šen-
tilj to Koper and A2 from Karavanke tunnel to Obrežje, 
with its densest stands on the A1 between Ljubljana and 
Blagovica, and between Vransko and Slovenske Konjice 
(Frajman & Kaligarič, 2009). It grows on road verges as 
well as in the central reserve.
Substrate sampling and salinity measurements
At the end of September and the beginning of Octo-
ber in 2009, we selected parts of Highway A1 (connect-
ing Šentilj and Koper, passing Maribor, Ljubljana) for 
the collection of plants and substrate samples. The road 
has two lanes in each direction and a central reserve 
overgrown by taller vegetation. The fi rst site was located 
1 km from the highway service area at Lukovica in the 
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Nina ŠAJNA et al.: DITTRICHIA GRAVEOLENS – HOW DOES SOIL SALINITY DETERMINE DISTRIBUTION, ..., 7–12
direction of Trojane. A dense stand of D. graveolens 
plants extended for several kilometers along the entire 
road verge. The second site was located at the Ravne 
service area near Kozina. No continuous stands were 
observed there. Individuals of D. graveolens were found 
in smaller, discrete groups, only occasionally in dense 
stands along shorter road segments. 
Substrate samples were collected directly at the road 
margin to a maximum of 50 cm away, as the closest 
sample to the road, and then at distances 100 cm, 120 
cm, and 200 cm perpendicularly to the road margin. 
In this direction, a prominent gradient in plant height 
was observed (Fig. 1). At both locations, soil samples 
were collected from plots where D. graveolens was 
present. We collected 1 kg of substrate sample on each 
site for salinity analysis. For the two control samples, we 
collected the substrate at Kozina from sites where no D. 
graveolens individuals were sighted. 
Samples were sieved to remove larger stones, mixed 
with deionized water in a ratio of 1:9 and shaken for 1 h. 
The conductivity of the prepared solution was measured 
by a portable conductometer MA 5950 (Metrel, Slove-
nia) at room temperature (20 °C) after the solution had 
been allowed to settle for 30 min. Conductivity readings 
were corrected regarding the temperature at which they 
were taken, if necessary. 
For comparison of substrate salinity along the dis-
tance away from the road, a Welch-ANOVA was used to 
test for signifi cant differences, since the results yielded 
heterogeneous variances according to Levene’s test. 
Reproductive potential of D. graveolens
In evaluating the reproductive potential of D. gra-
veolens plants, we recognized three categories of plant 
height: 1 – from 5 to 15 cm; 2 – from 16 to 25 cm; 3 
– larger than 25 cm. The potential reproductive success 
of D. graveolens plants was estimated by counting the 
number of fl ower heads per plant in each category. Av-
erage seed (achene) number per single fl ower head was 
estimated after counting seeds for 50 randomly selected 
fl ower heads for each height category, which were 
collected in Lukovica. The data obtained were used for 
calculating the total seed number for an individual plant. 
RESULTS 
Observation on sites with D. graveolens stands 
showed that plant height and plant density increase with 
distance from the road margin. Differences were also 
observed in the abundance of D. graveolens plants be-
tween the Lukovica and Kozina locations. Additionally, 
as expected, those sites without D. graveolens in Kozina 
showed the lowest salinity values. 
The salinity of the substrate at Lukovica changed 
signifi cantly within the 2 m distance next to the road 
(Welch ANOVA at p>0.05; Fig. 2), because of lower 
salinity fi gures at a distance of 1 m. However, if we 
exclude those measurements within 50 cm of the road, 
an increase in salinity was observed from 1 m to 2 m 
away from the road margin – in the same direction as 
plant size increased. Up to 50 cm away, individual 
plants were 5 to 15 cm tall; from 1 to 1.5 m distance 
from the road, plants reached 10 to 30 cm of height, 
Fig. 1: Increasing height of Dittrichia graveolens indi-
viduals away from the road margin at the Lukovica site.
Sl. 1: Višina osebkov vrste Dittrichia graveolens narašča 
z oddaljenostjo od cestnega roba na lokaciji Lukovica.
Fig. 2: Mean salinity values of the substrate away from 
the road margin were signifi cantly different within the 
2 m distance (Welch ANOVA, p<0.05) at the Lukovica 
location. Different letters indicate signifi cantly differ-
ent means.
Sl. 2: Srednje vrednosti slanosti substrata so se statistič-
no značilno (Welcheva ANOVA, p<0,05) razlikovale z 
oddaljenostjo od cestnega roba znotraj razdalje 2 m na 
lokaciji Lukovica. Različne črke označujejo statistično 
značilno različne srednje vrednosti. 
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Nina ŠAJNA et al.: DITTRICHIA GRAVEOLENS – HOW DOES SOIL SALINITY DETERMINE DISTRIBUTION, ..., 7–12
and more than 2 m away, some individuals were taller 
than 40 cm. Plants grew in soils with salinity from 110 
to 237 µS/cm at both locations. Average soil salinity on 
two sites in Kozina without D. graveolens plants was 97 
and 82 µS/cm.
Dittrichia graveolens plants showed high reproduc-
tive potential, which increased with the plant’s height 
and differed signifi cantly among height categories 
(Welch ANOVA, p<0.05; Fig. 3). The average number of 
seeds (achenes) in a single fl ower head was 30 seeds, and 
it showed low variability among individuals of different 
size. According to that, estimated seed production of 
plants was about 90 seeds per plant in the fi rst and 4380 
seeds per plant in the third height category. In relation to 
distance to the road margin, in its near proximity plants 
produced on average 500 seeds; however, even at 1 m 
distance we found plants exhibiting high reproductive 
potential with more than 2000 seeds per plant. 
DISCUSSION 
Deicing chemicals, which help to improve road 
safety, are regularly used on Highway A1 during winter. 
However, we expected that on road segments toward 
the south of the country deicing salts would be less fre-
quently used because of the rarer incidence of snowfall 
and freezing conditions. Even though the sampling was 
rather simple, our results indicate that the occurrence 
of D. graveolens might be connected to increased soil 
salinity values. Less densely developed and not contin-
uously occurring D. graveolens stands were observed in 
the southern part of this motorway. On all the sites with 
D. graveolens plants, salinity was higher, while at values 
below 100 µS/cm, no plants were observed. Dittrichia 
graveolens, besides being halotolerant for soil salinity, 
has an additional competitive advantage over native 
plants: it is an annual species, surviving winter as seeds 
that can avoid the direct negative impact of saline spray, 
which perennial native species would have to endure.  
Additionally, the salinity gradient measured at the 
road verge corresponds with previous similar reports, 
showing a sharp decline in soil salinity over the fi rst 2 
m distance from salted roads (Thompson et al., 1986). 
Our results show that the saline opportunity habitat for 
D. graveolens is located only on a narrow strip 1 m or 
less from the road, up to the distance where the decline 
in salinity enables the native, more competitive species 
to begin to dominate the habitat. The rarer occurrence 
of D. graveolens in the southern part of the highway, 
which lies in a region with a sub-Mediterranean climate, 
suggests that the establishment of D. graveolens in less 
saline soil is limited because the species is a weak com-
petitor compared to native sub-Mediterranean species 
and not because of unsuitable climatic conditions. This 
is furthermore underpinned by numerous records of D. 
graveolens along the roads in those Central European 
countries (Kocián, 2015a) that have a rather cold cli-
mate. 
Our results also show that plants 1 m from the road 
were already 30 cm high, and these were the plants 
showing the highest seed production. Our previous 
studies on Aster squamatus, we stressed that one char-
acteristic that can be key for successful invasion of alien 
invasive Asteraceae, especially if they can become 
established in less productive habitats (including saline 
or semi-saline habitats), is the late onset of fl owering 
Fig. 3: Reproductive potential of D. graveolens plants, 
collected in Lukovica, from different height categories 
(1: 5–15 cm; 2: 16–25 cm; 3: >25 cm) measured through 
the number of fl ower heads per single plant. 
Sl. 3: Reproduktivni potencial D. graveolens na lokaciji 
Lukovica izmerjen kot število koškov na posamezno 
rastlino, ki so pripadale trem velikostnim razredom (1: 
5–15 cm; 2: 16–25 cm; 3: >25 cm).
Fig. 4: Dry fruiting Dittrichia graveolens plants at the 
Kozina location on 25th October 2009.
Sl. 4: Posušene plodeče rastline D. graveolens opazo-
vane 25. oktobra 2009 na lokaciji Kozina.
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Nina ŠAJNA et al.: DITTRICHIA GRAVEOLENS – HOW DOES SOIL SALINITY DETERMINE DISTRIBUTION, ..., 7–12
(Šajna et al., 2014; Šajna 2016). Dittrichia graveolens 
starts to fl ower in September, and fl owering lasts until 
October (Kocián, 2015a). 
We observed several dried fruiting plants at full 
height (Fig. 4). This is an indication that fully developed 
plants, able to produce seeds, are rarely impacted by 
mowing during road verge maintenance because mow-
ing happens too early and because larger plants grow 
in the depression of the road verge, away from the road 
margin. Location by the road represents immediate 
potential for seed dispersal via the slipstream of passing 
vehicles (von der Lippe et al., 2013), while the road 
corridor functions as a route of secondary dispersal. 
Such dispersal via traffi c, enabling very rapid and often 
unnoticed invasions, has been recorded for many inva-
sive plant species (von der Lippe & Kowarik, 2007). 
 ACKNOWLEDGMENTS
We thank two anonymous reviewers for their helpful 
comments and corrections, which improved the previ-
ous version of the manuscript. M. Kaligarič acknowl-
edges the support of the P1-0164 grant, funded by the 
Slovenian Research Agency.
DITTRICHIA GRAVEOLENS – KAKO SLANOST TAL DOLOČA NJENO RAZŠIRJENOST, 
MORFOLOGIJO IN REPRODUKTIVNI POTENCIAL?
Nina ŠAJNA 
Faculty of Natural Sciences and Mathematics University of Maribor, Koroška 160, Maribor, Slovenia
nina.sajna@um.si
Kristijan ADAMLJE
Marnova ulica 31, 1410 Zagorje ob Savi, Slovenia
Mitja KALIGARIČ
Faculty of Natural Sciences and Mathematics University of Maribor &
Faculty of Life Sciences, 2311 Pivola, Slovenia
POVZETEK
Soljenje cest pozimi pripomore k varnosti prometa, a ima močan vpliv na vrste, ki poseljujejo cestne robove. 
Ustvarja rastišča s slanimi tlemi, ki jih lahko poselijo rastline s posebnimi prilagoditvami in toleranco na slanost. 
Tak primer je avtohtona mediteranska vrsta Dittrichia graveolens, ki se ob cestnih robovih seli v osrednjo Evropo 
in jo najdemo že v mnogih državah. Proučevali smo, kako slanost tal določa višino rastlin D. graveolens, njihov 
reproduktivni potencial in razširjenost ob cestnem robu. Višina rastlin je bila odvisna od električne prevodnosti (EC) 
tal – merilo za slanost. Naši rezultati kažejo, da vrsta najbolje uspeva v tleh z vrednostmi EC med 110 in 170 µS/
cm, medtem ko je pri vrednostih pod 100 µS/cm nismo opazili. Uspeli smo identifi cirati tri velikostne razrede, ki se 
razlikujejo v reproduktivnem potencialu.
Ključne besede: invazivna vrsta, cestni rob, soljenje cest, Slovenija 
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REFERENCES
Brullo, S. & G. de Marco (2000): Taxonomical re-
vision of the genus Dittrichia (Asteraceae). Portugaliae 
Acta Biol., 19, 341-354.
Cale, P. & R. Hobbs (1991): Condition of roadside 
vegetation in relation to nutrient status. In: Saunders, 
D.A. & R.J. Hobbs (eds.): Nature conservation 2: The 
role of corridors, Surrey Beatty & Sons, Chipping Nor-
ton, pp. 353-362.
Frajman, B. & M. Kaligarič (2009): Dittrichia grave-
olens, nova tujerodna vrsta slovenske fl ore. Hladnikia, 
24, 35-43.
Gelbard, J.L. & J. Belnap (2003): Roads as conduits 
for exotic plant invasions in a semiarid landscape. Con-
serv. Biol., 17, 420-432.
Heger, T. &  H.J. Böhmer (2006): NOBANIS – In-
vasive Alien Species Fact Sheet – Senecio inaequidens. 
– From: Online Database of the European Network on 
Invasive Alien Species – NOBANIS www.nobanis.org. 
Date of access 23/11/2016
Jogan, N., T. Bačič, B. Frajman, I. Leskovar, D. Na-
glič, A. Podobnik, B. Rozman, S. Strgulc Krajšek & B. 
Trčak (2001): Gradivo za Atlas fl ore Slovenije. Center za 
kartografi jo favne in fl ore, Miklavž na Dravskem polju, 
443 pp.
Kocián, P. (2015a): Dittrichia graveolens (L.) Greuter 
– a new alien species in Poland. Acta Musei Silesiae, 
Scientiae Naturales, 64, 193-197.
Kocián, P. (2015b): Novelties in the roadside fl ora 
of Moravia and Silesia (Czech Republic) –1. Spergularia 
media. Acta Musei Silesiae, Scientiae Naturales, 64, 
263-267.
Lambdon, P.W., P. Pyšek, C. Basnou, M. Hejda, M. 
Arianoutsou, F. Essl, V. Jarosik, J. Pergl, M. Winter, P. 
Anastasiu, P. Andriopoulos, I. Bazos, G. Brundu, L. 
Celesti-Grapow, P. Chassot, P. Delipetrou, M. Josefsson, 
S. Kark, S. Klotz, Y. Kokkoris, I. Kühn, H. Marchante, I. 
Perglova, J. Pino, M. Vilà, A. Zikos, D. Roy & P.E. Hulme 
(2008): Alien fl ora of Europe: species diversity, tempo-
ral trends, geographical patterns and research needs. 
Preslia, 80, 101-149.
Pollnac, F., T. Seipel, C. Repath & L.J. Rew (2012): 
Plant invasion at landscape and local scales along 
roadways in the mountainous region of the Greater 
Yellowstone Ecosystem. Biol. Invasions, 14, 1753-1763.
Preston, R.E. (2006): Dittrichia. In: Flora of North 
America Editorial Committee (eds.): Flora of North 
America North of Mexico, Vols. 19-21. Oxford Univer-
sity Press, New York and Oxford, 473 pp.
Pyšek, P., P.W. Lambdon, M. Arianoutsou, I. Kühn, 
J. Pino & M. Winter (2009): Alien vascular plants of Eu-
rope. In: Handbook of Alien Species in Europe. DAISIE 
(eds.): Springer, pp. 43-61.
Smettan, H.W. (2002): Klebriger Alant (Dittrichia 
graveolens) und Verschiedensamige Melde (Atriplex 
micrantha) am Autobahnmittelstreifen in Südbayern. 
Ber. Bayer. Bot. Ges., 72, 111-116.
Šajna, N., M. Kaligarič & D. Ivajnšič (2014): Re-
production biology of an alien invasive plant: a case 
of drought-tolerant Aster squamatus on the Northern 
Adriatic seacoast, Slovenia. In: Rannow, S. & M. Neu-
bert (eds.): Managing protected areas in Central and 
Eastern Europe under climate change, Advances in 
global change research, Vol. 58. Springer, Dordrecht, 
pp. 279-288.
Šajna, N. (2016): Alien plant species invading rare 
and protected habitats in Slovenia. In: I.S. Travlos (ed.): 
Weed and pest control - molecular biology, practices 
and environmental impact, Nova Publishers, New York, 
pp. 35-54.
Scott, N.E. & A.W. Davison (1982): De-icing salt and 
the invasion of road verges by maritime plants. Watso-
nia, 14, 41-52.
Thompson, J.R., A.J. Rutter & P.S. Ridout (1986): The 
salinity of motorway soils. 2. Distance from the carriage-
way and other sources of local variation in salinity. J. 
Appl. Ecol., 23, 269-280.
Truscott, A.M., S.C.F. Palmer, G.M. McGowan, 
J.N. Cape & S. Smart (2005): Vegetation composition 
of roadside verges in Scotland: the effects of nitrogen 
deposition, disturbance and management. Environ. 
Pollut., 136, 109-118.
von der Lippe, M., J.M. Bullock, I. Kowarik, T. Knopp 
& M. Wichmann (2013): Human-mediated dispersal of 
seeds by the airfl ow of vehicles. PLOS ONE 8: e52733.
von der Lippe, M. & I. Kowarik (2007): Long-dis-
tance dispersal of plants by vehicles as a driver of plant 
invasions. Conserv. Biol., 21, 986-996.
Williamson, M., K. Dehnen-Schmutz, I. Kühn, M. 
Hill, S. Klotz, A. Milbau, A., J. Stout & P. Pyšek (2009): 
The distribution of range sizes of native and alien plants 
in four European countries and the effects of residence 
time. Divers. Distrib., 15, 158-166.
Wraber, T. (1999): Dittrichia. In: Martinčič, A., T. 
Wraber, N. Jogan, V. Ravnik, A. Podobnik, B. Turk & 
B. Vreš (eds.): Mala fl ora Slovenije, Tehniška založba 
Slovenije, Ljubljana, pp. 558.