Portulaca oleracea: Advanced Studies

Published: January 9th, 2011 | Updated: 17/01/15

In 1980, when driving with Prof. Benito Valdes from Madrid to Seville, I collected seeds of Portulaca oleracea as I often do. Later, I wrote an article on my findings of taxa related to [“Portulaca oleracea” P. oleracea] and my colleagues translated it into Spanish. It was published in the Spanish journal ‘Lagascalia.’ Following this article, my colleagues at the Madrid Botanical Garden asked me to write the item Portulaca oleracea which was published in Flora Iberica in 1990. In 1985, during my sabbatical year, I stayed in Talahasi, Florida and wrote an article on the distribution of the [Portulaca oleracea] aggregate in Florida. My co-author was a colleague from the Department of Botany at Florida State University.

I thought that there was no further point in continued study of the [“Portulaca oleracea” P. oleracea] complex and stopped collecting additional samples. I considered that there were few new paths I could take in this huge mosaic and abandoned this field until 2003, when our dear friends from California, Michael and Valerie Barbour, invited us to meet midway between America and Asia – in Tenerife, one of the Canary Islands. Michael had a budget to study spontaneous Canarian pine (Pinus canariensis) woodlands growing there long before the Jewish National Fund started to use this tree for forestation in Israel.
We shared his rented apartment; I rented a car and started to work. I wanted to investigate the relationships between species of the [“Portulaca oleracea” P. oleracea] complex and the altitude factor. I collected samples from all the accessible parts of the island. An excellent dissecting-microscope in the local university enabled me, during my time there, to discover unexpectedly high species diversity. Among others, the collection included Portulaca nicaraguensis, known at that time only from Central America. I started to write the article about the status of the complex in the Canary Islands. The material remained “dormant,” waiting for the chromosome counts of a few taxa collected there.

In the summer of 2004 a conference of our scientific organization OPTIMA took place in Belgrade. During the last days of the meeting Prof. Dr. Pertti Uotila asked me for my current opinion on the status of the entire group. He became the person responsible for editing the material of the [Chenopodiaceae] and [Portulacaceae] in the new Flora Europaea Atlas project. He asked me if I still held to the idea of sub-species as [http://flora.huji.ac.il/browse.asp?action=showfile&fileid=15111 we had written in 1978]. The alternative Pertti gave me was in seeing the complex as composed of independent species, like the Italian authors. From his comments in Belgrade I understood that in 2000, two Italian authors raised two of our subspecies to the species level.

Although I had previously decided to terminate my work with the complex, I returned to it, because I did not like this new situation. I revised the dormant manuscript on the complex in the Canary Islands, and waited for the additional expected information. I started to prepare material for a comparative article by visiting large islands in the Mediterranean Sea. I collected samples with the help of Giorgios Hadjikyriakou in Cyprus (Fig. 11.3.1), and concluded that several samples belonged to a species I do not know. I later described it as [“Portulaca cypria” P. cypria]. Another collection trip was in Crete with my friend Dr. Jacques Zaffran. My few collection days there concluded with a Cretan species later named P. zaffranii. In Cyprus we found remnants of the cultivar we considered as Portulaca sativa (Fig. 11.3.1). The plant differs from all other species known, by its large seeds (1.1 mm in diameter and more; Fig. 11.3.2; [useful_plants_k2 Figs. 11.1.24, 11.1.25, 11.1.29]). The seed surface of the cultivar in Cyprus resembles that of P. zaffranii (Fig. 11.1.12) and P. rausii (Figs. [useful_plants_k1 11.1.11], [useful_plants_k2 11.1.18]).

Fig. 11.3.1: Seeds and parts of capsules of P. sativa in a field near Nicosia, Cyprus.

[“Portulaca oleracea” P. oleracea] is known in Greek as “glystrida”. Searching for that name in Google, one reaches a restaurant in Athens. In addition, plenty of restaurants are mentioned, that serve Greek Salad with glystrida. The need to know that name developed quickly when I began to collect its seeds in Crete. The plant is totally synanthropic (ecologically connected with human activity), therefore the safest place for systematic collection was in, or near to towns and villages. The best sites in these places were rose gardens of the local gasoline stations. The roses were irrigated in spring, and in most cases were not hoed later.
Hence, when I arrived, [“Portulaca oleracea” P. oleracea] plants were waiting for me: they had received light, moisture and high soil temperatures for germination and development. The plant’s pre-adaptation to open places in tropical savannas enabled it to become cosmopolitan. All the Cretans passing by me knew the plant, as they collect it for their salad, but they wondered what this stranger was doing here. I was often asked, in Greek (which I do not understand), what I was doing. My answers in English “It is for the University” or “for science” did not help. A stranger collecting old and dirty plants did not seem logical to them. J. Zaffran, who speaks Greek very well, taught me to say in Greek that I am a botanist: E mae botanologo, or votanologo. When I said these magic words a big smile came to the person’s face and he would continue on his way. This variety of human being was already well known to them.

Following the OPTIMA meeting in Belgrade, I returned to more intensive work on the [“Portulaca oleracea” P. oleracea] issues. I altered the Canary Islands manuscript and submitted it to the editor of Willdenowia, Dr. Norbert Kilian, in September 2004. It seems that I caused him much work editing my article on Arundo (published that year in Willdenowia). I did not hear from him, and waited tensely but patiently. Meanwhile, the committee dealing with the preparation of Prof. Werner Greuter Festschrift, suggested expanding the Canary Islands manuscript by adding a genomic (DNA) study of the [“Portulaca oleracea” P. oleracea] group.
Talking about it with Dr. Kilian and Dr. Raus from the Berlin Botanical Garden and Museum, they told me of a new, enthusiastic scientist heading the laboratory there: Dr. Birgit Gemeinholtzer. She was ready to assist me in this work. A European research fund (SYNTHESIS) supported my visit in Germany financially. We were hoping that my results would be supported by the DNA-methods. Birgit was surprised to learn about my expectations and said that only after about three years of PhD-student research are results (perhaps) obtained. I did not succeed in offering a study of principles (e.g. of polyploidy complexes) or other fundamental questions, that will be researched and answered through the Portulaca research. Birgit said that without such questions there is no sense in submitting a research proposal. She knows what she is saying, as she has been successful in submitting proposals that received financial support. Norbert, who was involved in the recommendation for the SYNTHESIS support, expected me to give a program for a PhD thesis in which I would be the principal tutor; Birgit would be assisting “my” student and me in an issue that is out of her main field.

Birgit is working on the DNA of plants in the [https://flora.org.il/en/plants/systematics/compositae-asteraceae/ Asteraceae] (the sunflower family). The date of my return and hence the date of my SYNTHESIS lecture was fixed but the results of the DNA analysis had not yet come. A short time before the lecture I got results summing up, briefly, that there is no proper differentiation, and that all the samples of “my” different taxa look similar in the DNA analyzed. I fulfilled my duty for SYNTHESIS but had nothing new to report. At the end of the lecture Thomas Raus talked with me and suggested a way to carry on with my research in the OPTIMA research system: let us name the group of taxa related to [“Portulaca oleracea” P. oleracea] as an aggregate, and below it we’ll list the temporary species and regard them as “microspecies.” Prof. Benito Valdes agreed to accept the manuscript, after proper review, for the Spanish journal ‘Lagascalia,’ which concentrates on Spanish flora, and Tenerife is part of Spain. I altered the manuscript to fit the new level of microspecies and the comments of Th. Raus. The article was published in 2006 in Spain. I raised there all “my” subspecies of P. oleracea to the microspecies level. The time of my retirement was approaching and I started to think of what to do as a retiree. I thought of [“Portulaca oleracea” P. oleracea] aggregate as a strong horse on which I would gallop directly into my retirement. I decided to complete my studies in the Canary Islands, travel from there to Cyprus, to Crete, to additional islands in the Mediterranean, to Madagascar, and to the largest of all – the island-continent Australia. It seems that the dreams were good, but it was not yet clear what I had found in these microspecies of the aggregate.

In the summer of 2005 I went to Bologne, Italy, to search for the typical plant of Arundo plinii which had become part of my expertise. I suggested to Prof. Reimondo, the “Botany King” of Sicily, that I would come to visit Palermo and collect Arundo and [“Portulaca oleracea” P. oleracea] within three days. This was in order to compare the findings with those of Tenerife, Cyprus and Crete. Dr. Gianniantonio Domina took me around in his car and we found that all the “Arundo plinii” of Sicily was in fact Arundo collina, which created continuous “lawns” on clayey slopes over thousands of square kilometers. On the second day I identified the 16 populations of [“Portulaca oleracea” P. oleracea] aggr., that I had collected during the first day. I found a new form that was later photographed by the SEM in Palermo. The bottom line was that there was going to be a new-to-science microspecies which would become Portulaca sicula. In addition I also determined six microspecies already known. I gave a lecture to the doctorate students of the department of botany in Palermo on Arundo; later I gave them a lecture on the [“Portulaca oleracea” P. oleracea] aggregate. Prof. Raimondo came for a visit of a few minutes. He is the chairman of the Department of Botany, The Head of the Botanical Garden, and the Dean of the Faculty of Science and the time he dedicates to things can show his appreciation of the subject. We had lunch together on my last day there and enjoyed a 3-hour scientific conversation on our mutual article. These three hours were a real gift.

A few days after returning from Sicily I went to the island of Rhodes. An international conference of cancer researchers (ISOBM) was taking place, and my former student, Prof. Vivian Barak was the president of that conference. I justified my participation by presenting a lecture on “The Flora of the Shroud of Turin,” which was far removed from the subject of all the other lectures of that conference. I collected many samples of [“Portulaca oleracea” P. oleracea] aggregate and the collection assisted in promoting the entire project. I found there Portulaca rausii, a microspecies new to science. My first observation of this taxon was on a visit to the Berlin Botanical Garden, where I detected the special features of the plant collected by Thomas Raus in Santorini, the Aegean Island. I could not count chromosomes of the Santorini specimen as it was fumigated before being put into the herbarium. Finding the plant in Rhodes and in Sicily enabled us to count the chromosomes of this microspecies and to include it in the new manuscript.

In 2008, [http://flora.huji.ac.il/browse.asp?action=showfile&fileid=31794 the article] on the aggregate of the microspecies related to [“Portulaca oleracea” P. oleracea] in large Mediterranean islands was published in the botanical journal of OPTIMA in Palermo. The insertion of all the 15 microspecies known, into one article, brought much order to the complex. The reviewers of the manuscript brought to our attention that following an in-depth study and typification of Linnaeus’ herbaria, the type specimen of Portulaca oleracea in the narrow sense, is the one that looks like [useful_plants_k3 Fig. 11.2.12]. Hence, the name Portulaca stellata became a synonym. The typical plant, according to my older perception, from Hortus Cliffortianus, now became nameless. My reviewers recommended providing it with a new name that would be different enough to avoid confusion. We selected the prominent property of the seed morphology ([useful_plants_k3 Fig. 1.2.12]) which is three tubercles on elongated epidermal cells, and named it Portulaca trituberculata.

At the end of December 2009 I received a letter from Dr. Giovanna Bossi from Modena, Italy, containing an article about the ethno-botany of [“Portulaca oleracea” P. oleracea] authored by her and her colleagues. In her letter Giovanna added thanks for my previous work on that plant. In addition to more information on various aspects of utilization and common names of the plant in Italy, the authors brought information from their study of some 700 seeds derived from archaeological sites in Emilia Romagna not far from Bologne. On my request Giovanna sent me all the seeds and this led me to find interesting information encoded in the seeds’ identity. It seems that I began to have the entire picture for part of the microspecies relationships. Portulaca trituberculata is found in all the sites investigated. In Ferrara, [“Portulaca cypria” P. cypria] begins to appear in one of the samples from the 11th century. P. sativa is represented in the same dig, at a higher (thus younger) level. On my earlier visit to Cyprus with Mr. Hadjukyriakou, in a field with P. sativa (Figs. 11.3.1, [useful_plants_k2 11.1.25]) he taught me how the seed epidermis looks. A visit to the herbarium of Geneva in July 2006 taught me that in Switzerland in the 1800’s, people grew P. sativa that looks like [“Portulaca cypria” P. cypria] (Figs. 11.3.2, 11.3.3). I was left with a nomenclatural question – what did Haworth, the author of P. sativa see, when describing the plant. I thought I was close to the answer – I had to see the seed surface of the plant from the herbarium of the British Museum, London.

Fig. 11.3.2: A seed of P. sativa from a herbarium specimen collected in Switzerland in the 1800’s and deposited in Geneve.

Fig. 11.3.3: A close up to a part of Fig. 11.3.2.

However, the museum is far away from Jerusalem and requests from colleagues to have the material on loan did not bring about the desired result in 2009 and 2010. I decided to invest more efforts in verifying the status of Portulaca sativa in the British Museum. I phoned them and asked for a clear answer; it came a few days later and it was negative. There was no original material of that species there. I first saw a specimen of Portulaca sativa in 1978, when I visited the herbarium of the University of Cornell, USA. I was impressed by the large seeds, more than 1.1 mm in diameter, but I was rather limited in time then. My wife Drora and our children Morit and Barak were waiting for me nearby. Prof. Allan Witztum, our friend, who accompanied us, invited me to see the campus of Cornell University. I could not stop and Allan bought and gave me a few postcards to enable me see what I missed. I also missed the opportunity to have a closer look at seeds of P. sativa in Asa Gray’s Herbarium. Asa Gray was one of the greatest botanists at the end of the 19th century.

In the summer of 2010, when I returned, to search for seed morphology of the cultivars, Prof. Witztum informed me that he was visiting Cornell again for a short time. I asked him to return to the herbarium I visited in 1978 and get me a few seeds on loan. His attempts failed. Among other things Allan is very good at literature research and soon after that he informed me that the researcher Haworth dealt with succulent plants at the beginning of the 19th century. He did not press and save the typical plants (holotype) that he used for the description of new species he described. The heir of his scientific material did not preserve any relevant material at the herbarium in Oxford. When consulting with my colleagues in Europe I understood that I have to select a new type (“neotype”) to Portulaca sativa.

Fig. 11.3.4: A seed of P. sativa from a herbarium specimen collected in Rome (1828) and kept in the herbarium of La Sapienza University, Rome.

Recalling that I have seen in Geneva many herbarium sheets of P. sativa I decided to select a neotype from them. My basic assumption was that if I find that several large herbaria in Europe have considered the Swiss type as P. sativa since the 19th century, I’ll follow them and make one of the specimens a neotype. Dr. J. Walter from Vienna, a new colleague of mine, sent me material collected in 1858 in Germany and it agreed with the Swiss form. Seeds of a specimen collected in 1828 in Rome by Sanguinetti shared the important morphology (Fig. 11.3.4) with the Swiss type. I therefore concluded that the true *P. sativa is represented by the Swiss type.