This contribution will contain a growing list of interesting and typical plant species that I’ve seen in (outdoor) flower pots in Vienna and its surrounding. Some of them are very rare or even first discoveries. Special attention will be paid to the relevancy of imported flower pots in the introduction and spread of neophytes, especially by reporting tangible evidence.
The entry can be regarded as a successor of the works of Hoste et al. (2009) and Brandes (2017) dealing with the situation in Belgium and Northern Italy / Northern Germany, respectively. It is easy to see that there are many similarities. But some information will be very different, too.
Asteraceae
Eclipta prostrata
An extremely rare neophytic species only recently reported for the first time in Austria (Barta et al. 2019). Seen by me in a flower pot with Euonymus fortunei of a Schanigarten in Vienna’s 1st district and in the outdoor garden department of a DIY warehouse, as a weed in tarmac cracks, alongside with Cyperus eragrostis.
Erigeron bonariensis
Repeatedly seen in flower pots, and they can be considered as an important vector for the distribution of this species. On two occasions it has been found in flower pots with lavender (see below) in one year and in their surroundings in the next, strongly indicating a spread. However, being anemochorous, Erigeron bonariensis may be invading flower pots from their surrounding, too.
Erigeron sumatrensis
Repeatedly seen in flower pots, and they can be considered as an important vector for the distribution of this species. However, being anemochorous, Erigeron sumatrensis may be invading flower pots from their surrounding. too. Remarkable detail: One of the first larger stands of Erigeron sumatrensis I’ve seen grew in a front garden in Vienna’s 2 district alongside with cultivated tarragon (Artemisia dracunculus). Both species have a strong resemblance, and I tend to believe that the existence of this Erigeron stand had to be accounted by the confusion with the tarragon. This is not an uncommon phenomenon that can further the spread of a weed considerably.
Gamochaeta pensylvanica
Syn. Gnaphalium pensylvanicum. Seen twice in flower pots, and at another site in the wild quite far away from from the other ones, but rich in flower pots, too. So flower pots can be considered an important if not the only vector for the introduction of Gamochaeta pensylvanica in Vienna.
Laphangium luteoalbum
Syn. Gnaphalium luteoalbum, Helichrysum luteoalbum. A strongly endangered indigenous plant and a character species of dwarf rush-communities (Isoeto-Nanojuncetea), Laphangium luteoalbum now sometimes occurs in flowerpots, garden centers and other garden-like places. Among others, it has been seen by me in the Botanical Garden of the University of Vienna, in the bed of cacti and other succulents, alongside with Euphorbia maculata and E. humifusa, showing that it can tolerate remarkable dry conditions. I’ve also recently seen it in a pavement crack of a residential area in Neunkirchen (Lower Austria), where it most certainly had been introduced with flower pots in one of the adjacent gardens.
Sonchus tenerrimus
The first finding in the wild of Vienna and Austria took place almost 15 years ago (2006: Rožánek in Adler et al. 2008). It was recovered by me in 2019 and 2021, but in flower pots only. So it doesn’t seem to have a significant tendency towards spreading.
Symphyotrichum squamatum
Seen three times in Viennese flower pots so far, and they can be considered as an important vector for the distribution of this species. In fact, the observations in flower pots were the first ones in Austria, and the first finding of Symphyotrichum squamatum in the wild was probably an offspring.
Euphorbiaceae
Acalypha rhomboidea
Only provisorically identified, this species has been found twice in Viennese plant containers with Trachycarpus fortunei. A cursory research revealed at least that the specimens found neither belong to Acalypha australis nor to A. virginica, whereas they fit the descriptions of Acalypha rhomboidea very well. More Information upcoming.
Euphorbia subgen. Chamaesyce
Similar to the Oxalis species, the species of Euphorbia subgen. Chamaesyce, to which the species listed below belong, have explosive fruits that allow them to literally jump from flower pot to flower pot and into their surroundings (Hügin et Hügin 1997).
Euphorbia maculata
A rather common plant in flower pots with many different species, a context between such occurences of Euphorbia maculata and those in their surroundings has been watched several times. However, the direction of the exchange isn’t always clear. It was obvious sometimes that Euphorbia maculata with its explosive fruits reaches places several times higher than the plants themselves.
Euphorbia prostrata
Today a moderately common plant in flower pots of many species, especially in those of Trachycarpus fortunei and Begonia spp. A direct connection between flower pot occurences and those in their surroundings has been watched a few times.
Euphorbia serpens
Today a moderately common plant in flower pots of many species, especially in those of Trachycarpus fortunei. A direct connection between flower pot occurences and those in their surroundings has been watched a few times. One occurence was particulary interesting: a Schanigarten in the Mariahilfer Straße (Vienna) had several flower pots with Trachycarpus fortunei for ornamental purposes. In them grew several specimens of Euphorbia serpens and E. prostrata as well as of Cyperus rotundus. Both of the Euphorbia species made it onto the adjacent sidewalk and tramway track, where, close by, three other sociologically related species already grew: Dysphania pumilio, Eleusine indica and Euphorbia maculata.
So here we have the case of the rapid sociological emergence of an unusually richly developed stand of a plant community – the Eleusinetum indicae – by the encounter of two completely different vectors. Since all of the species mentioned are still spreading, this also can be considered as a preview into the future of Central Europe, in which such species-rich stands will become increasingly common.
Absent Euphorbia Species
With Euphorbia subgen. Chamaesyce it is also interesting which species are present in the region of Vienna but totally absent from flower pots: Euphorbia humifusa, E. glyptosperma and E. nutans. Euphorbia humifusa is moderately frequent in East Austria, escpecially in smaller towns around Vienna. It isn’t listed by Hoste et al. (2009) and Brandes (2017), either. The same applies for E. glyposperma, rare in Austria, whereas E. nutans – extremely rare if not extinct in the greater area of Vienna – has been reported by Brandes (ibid.) from the region of Lake Garda.
In addition, Euphorbia chamaescye, another Chamaesyce species and one that is supposed to be indigeneous to the northern Mediterranean, is absent not only from the region of Vienna, but also from the flower pots in the areas researched by Hoste et al. (2009) and Brandes (2017).
All of these species are ecologically and sociologically extremely similar to those listed above. Yet something that isn’t obvious must be different with them.
Oxalidaceae
Similar to Euphorbia subgen. Chamaesyce, the Oxalis species have explosive fruits that allow them to literally jump from flower pot to flower pot and into their surroundings.
Oxalis corniculata
This is a very common plant species in East Austria and by far the most common one in flower pots.
Oxalis dillenii
The second most common Oxalis species in East Austria and in flower pots.
Oxalis stricta
Often thought of as a rather common plant species, it it surprisingly rare in East Austria. At least today: it might have been replaced by Oxalis corniculata and O. dillenii. Only seen in flower pots in a leisure area on the Donauinsel, Vienna, in several plant containers with Trachycarpus fortunei, accompanied by the mentioned Oxalis species, and once by Acalypha rhomboidea.
Oxalis triangularis
This is a rather common ornamental plant, both in its green and red leafed variant. It is often planted as an undergrowth in containers with trees or shrubs. Due to its explosive fruits, it is impossible to tell wether plants found in containers are cultivated or subspontaneous. An escape into the wild has been watched by me in Vienna’s 18th district. Here it grew in a lawn a few yards aside from the putative mother plant. Oxalis triangularis is not supposed to be winter-hardy in Central Europe, though, and the mentioned plants didn’t survive.
Oxalis pes-caprae
Seen in a plant container with Trachycarpus fortunei once, in Viennas 9th district. In the Mediterranean a very common weed, Oxalis pes-caprae is not supposed to be winter-hardy in Central Europe. Therefore, although this finding might be the first in Austria, the species shouldn’t be considered a part of Austria’s wild flora.
Cyperaceae
Cyperus eragrostis
Seen once in a Viennes flower pot containing Trachycarpus fortunei so far. And in a garden center in Vienna I’ve found it for sale, under the name Cyperus alternifolius. While the latter is a rather common indoor ornamental plant species, I haven’t found any evidence that Cyperus eragrostis – a species generally considered as a weed – is cultivated, too. I tend to believe that it just invaded flower pots that originally held Cyperus alternifolius, and the latter eventuelly vanished. Whether or not the dealer and his employees noticed that the plant had been replaced, I wouldn’t know. But one has to admit: Cyperus eragrostis is rather attractive. Furthermore found in the outdoor garden department of a DIY warehouse, as a weed in tarmac cracks, alongside with Eclipta prostrata. So, a connection between the spontaneous populations and flower pots seems to be plausible.
Cyperus esculentus
Found in 2018 independently by Essl (Essl et al. 2018) and me (unpublished) in a flower pot containing Trachycarpus fortunei at the Karlsplatz, and in 2020, again by me in a flower pot containing Trachycarpus fortunei, at another site. So far no direct evidence of escaping from flower pots have been seen by me.
Cyperus rotundus
Judged by the vegetative features of the plants that rarely flower here, Cyperus rotundus is by far the most common of the three Cyperus species seen in flower pots by me in the area of Vienna. It also has been found repeatedly in garden centers. Most common vector plant, again, ist Trachycarpus fortunei, followed by Olea europaea.
Cyperus rotundus is one of the few species with which the escaping into the wild has been watched very conclusively: flowering specimens grew in a Trachycarpus pot, the palm tree eventually died and its pot was put aside. Upon visiting the site an year later, I found Cyperus rotundus in the devastated lawn near to the place where the pot had been put, aside with Trachycarpus fibres and flower pot earth. So obviously the pot was overturned at one time, losing part of its contents onto the lawn. Whether the offspring of Cyperus rotundus resulted from bulbs or seed, remains unclear, though.
Poaceae
Eleusine indica
Although Eleusine indica is moderately frequent in Vienna, I haven’t seen it in flower pots until summer 2021. Then I found it at two closely related sites at the Donaukanal in flower pots holding Citrus cf. japonica and Trachycarpus fortunei. A little bit earlier I’ve seen it in Baden (Lower Austria), where it grew in a pavement crack in front of a florist’s. This strongely indicates that flower pots may be a vector for Eleusine indica.
Muhlenbergia mexicana
September 2021: occurrences of Muhlenbergia mexicana have repeatedly been reported as connected to container plants or gardens (for a summary see Verloove 2011). I can add two observations to this: Muhlenbergia mexicana has been seen by me in flower pots of a Japanese restaurant’s Schanigarten in Vienna’s 1st district in 2020/2021 and next to flowerbeds in a newly built quarter of the 2nd district in 2021. The accompanying ornamental plants were very different from each other.
Update 03 September 2023: new findings of Muhlenbergia mexicana have been made in Vienna, including one each in a flowerpot with Nerium oleander or Pelargonium species. Altogether Muhlenbergia mexicana here is a plant that shows no affinity to specific “host plants” at all, which is uncommon and raises questions regarding the origin of both Muhlenbergia and the cultivated plants. In one case spread from a flower pot into the crack of an adjacent sidewalk has been seen.
Poa infirma
Story from home: this delicate grass species had once been introduced into my household with a flower pot bought in a Viennese garden center. Poa infirma spread freely into the pavement cracks of the terrace of my appartement, and might still be living there. I didn’t. But Poa infirma insisted on accompanying me to my next two residencies. Althogether it stayed with me for about 15 years, jumping from flower pot to flowerpot, thus showing its ability to spread. Since it is extremely similar to Poa annua, it might have been overlooked in many places.
Other Families
Amaranthus blitum ssp. emarginatus
Amaranthus ssp. emarginatus is a neophyte that is spreading rapidly in Vienna and has been seen by me several times in Lower Austrian settlements, too. It can be found in flower pots and garden centers, and the connection between such occurences and those in their surroundings is sometimes very clear. All of the findings belong to Amaranthus blitum ssp. emarginatus var. gracilis – the Variant common to Austria – except one recent one that showed the features of var. emarginatus.
Chlorophytum comosum
Chlorophytum comosum is a common indoor ornamental plant and not winter-hardy in Central Europe. It has the unusual trait of inflorescences that also provide vegetative propagation by bending their tips to the earth, rooting, producing new plants and then withering. It can reach adjacent flower pots if they are close enough, and I have watched such an early step of getting spontaneous in Trachycarpus fortunei containers of an Viennese Schanigarten. Being “flower pot only”, the species shouldn’t be considered a part of Austria’s wild flora, although this finding might be the first in Austria.
Commelina communis
Commelina communis is a common ornamental plant. It is frequently used on balconies and window sills or similar small-scale structures, or in front gardens, and the origin of subspontaneous occurences is often obvious. It is not uncommon though, that the degree of spontaneity of Commelina communis stands is hard to access. Overall, it is rather clear that flower pots are the most important vector for the introduction of this species.
Lepidium didymum
Syn. Coronopus didymus. A rare neophyte in Austria, though I noticed this year that it isn’t as rare as thought. Seen among others in two cities in Lower Austria, in the pavement cracks of a garden center and of a residential area, respectively. So, although not seen in flower pots yet, this way of introduction is plausible.
Parietaria judaica
A species that seems to be spreading in Vienna, although it might has often been confused with the very similar and common Parietaria officinalis and thus overlooked. Parietaria judaica is one of the more frequent rare neophytic weeds in flower pots and plant containers in Vienna, but I haven’t seen it in their surroundings. I’ve found it in some front gardens in Bratislava and in a similar site in Vienna, though, typical places for the introduction of “flower pot spreaders”.
Polycarpon tetraphyllum
So far only once seen by me in a flower pot, one that I bought myself in a Viennese garden center. The respective flower was kept inside, and the plant didn’t come to flowering. However, Polycarpon tetraphyllum is spreading extremely fast in Vienna in these years, and I have found it on several locations in Lower Austria, too. The pattern of distribution in Vienna is rather random, which is typical for “flower pot spreaders” since flower pots are almost everywhere in inhabited areas.
Relevant Vector Plants
Trachycarpus fortunei
Trachycarpus fortunei is the most important vector plant in Vienna. Typical species groups growing in its pots are Cyperus spp., Euphorbia subgen. Chamaesyce spp. and Oxalis spp. Trachycarpus fortunei is a neophyte itself, and flower pots the most important vector, since this palm tree species is rarely – though increasingly – planted out in the gardens and parks.
Olea europaea
Olea europaea is the second most important vector plant in Vienna. Apart from the species listed with Trachycarpus fortunei that occurence in significant lower abundance here, several very rare neophytes such as Sonchus tenerrimus have been seen in its flower pots.
Ficus carica
Similar to Olea europaea regarding its flower pot weeds.
Lavandula angustifolia
This is a moderately common plant in Schanigärten, escpecially in those run by restaurateurs originating from the Mediterranean. Remarkably, I can recall only one notable plant species from flower pots with lavender: Erigeron bonariensis. But this species I’ve found several times, and in completely different parts of Vienna.
Begonia spp.
Ornamental plants of this genus are specifically important as vectors of the above listed Euphorbia species. They are very likely the most important vectors of them in Austrian graveyards. More rarely they are used in the streets, for instance in tree pits. On one of these occasions Euphorbia prostrata has been found on a parking strips right beside such a growing.
References
Adler, Wolfgang, Mrkvicka, Alexander, Fischer, Manfred A., mit Beiträgen von Dietrich, Gregor, Rožánek, Rudolf (2008): Nachträge zur „Flora Wiens“ (III.) – Neilreichia 5: 173–180.
Brandes, Dietmar (2017): Unkräuter der Containerpflanzen – Über einen „neuen“ Weg der Ausbreitung von Gartenunkräutern und Adventivpflanzen – Flor. Rundbr.: 48–68.
Essl, Franz, Follak, Swen, Raabe, Uwe, Barta, Thomas (2019): Cyperus esculentus – in: Gilli, Christian, Pachschwöll, Clemens, Niklfeld, Harald (Eds.): Floristische Neufunde (305–375) – Neilreichia 10: 217–219.
Hoste, Ivan, Verloove, Filip, Nagels, Cécile, Andriessen, Leo, Lambinon, Jacques (2009): De adventievenflora van in België ingevoerde mediterrane containerplanten – In: Dumortiera 97: 1–16.
Hügin, Gerold, Hügin, Heide (1997): Die Gattung Chamaesyce in Deutschland – Bestimmungsschlüssel, Wuchsorte, Fundortskarten und Fragen zur Einbürgerung. – Ber. d. Bayer. Bot. Ges. 68: 103-121.
Verloove, Filip (2011): Muhlenbergia mexicana – On: Manual of the alien plants of Belgium. – URL: http://alienplantsbelgium.be/content/muhlenbergia-mexicana [accessed 28.09.2021].
Authorship, Entry History, Acknowledgements
Authorship: © Rolf Diran 2021. Published on 25 September 2021. Last edited on 3 September 2023.