Pehr Forsskål – brilliant Swedish scientist

In scientific literature, Forsskåls name appears in many different forms, among others Forsskaal, Forsskal, Forskål, Forsskåhl, Forskåhl, and Forskaol, and his Christian name as Pehr, Per, Peter, Petter, and Petrus. In this paper, I have used the form Pehr Forsskål. He was born in Helsinki on January 11, 1732, being the youngest son of Johann Forsskål, who was a clergyman. His mother died, when he was only three years old. In 1741, the family moved to Uppland, where his father was appointed.

In those days, it was customary for sons of prominent citizens to start university studies at an early age. In 1742, when Pehr was only 10 years old, he and his two brothers were enrolled at the University of Uppsala. However, their father’s income was only sufficient to pay for two of the sons, and as Pehr was the youngest of the three, he was instead taught by the father himself, in subjects like theology, philosophy, Greek, Hebrew, and Latin. Pehr was indeed a gifted person. When he was only thirteen years old he was able to write letters in Hebrew.

In 1751, because of his “outstanding knowledge”, he was granted a scholarship for seven years of studies, five years in Uppsala, and two years at a European university, of his own choice. In those days, you studied broadly, and Pehr’s subjects were theology, philosophy, and natural sciences. The same year he passed his grade in theology. At an early stage, his interest in natural sciences lead him to be an acquaintance of Linné, whom he quickly came to admire. Forsskål studied various natural subjects, e.g. the metamorphosis of insects.

As Forsskål had a great interest in Oriental languages, orientalist Carl Aurivillius recommended him to study at the University of Göttingen, where orientalist Johann David Michaëlis was employed as a professor. At this university, in 1753, Forsskål began studies of philosophy and Oriental languages. In 1756, he graduated as a doctor of philosophy, defending a thesis named Dubia de principiis philosophiæ recentioris (’Doubts about the principles of newer philosophies’), in which he was criticizing Wolffianism, which in those days was the most popular philosophical doctrine. The same year he returned to Uppsala, where he wanted to study economics, agriculture, and natural sciences.

At this time, the ruling party in Sweden was Hattene (’The Hats’) – thus named because of the hats that the members of this party were wearing, as opposed to members of another party, Mössorne (’The Caps’). Censorship was widespread – a state which Forsskål found extremely unsatisfactory. In May 1759, he submitted an application to dispute on a paper of his, called De libertate civilii, which, simultaneously, was to be published in Swedish, titled Thoughts about civil freedom. This paper contained permissive thoughts, requesting political and economical freedom, as well as freedom of press. To write a controversial paper in Latin is one thing, but to publish it in the common language was an entirely different matter, unheard of in those days. The day the paper was printed, Forsskål himself distributed the 500 Swedish copies among the students of the university. When members of ’The Hats’ read the paper, they instantly forbade distribution of it, but it was already too late. Many people got acquainted with these new thoughts, and the paper contributed strongly to the abolition of censorship, which took place in 1766. However, at that time Forsskål was long dead, and thus didn’t see the result of his efforts.

Danish King Frederik V and his minister of foreign affairs, a German named Johann Hartwig Ernst von Bernstorff, were both eager patrons of this achievement of new knowledge. In 1756, Professor Michaëlis in Göttingen sent a letter to his fellow-countryman in Copenhagen, suggesting that the Danish king should send an expedition to Yemen in southern Arabia – since ancient times known as the legendary Arabia Felix (’Happy Arabia’). He stated his suggestion, writing the following: “Nature in this land is still rich in gifts, which are unknown to us. Its history goes back to ancient times; its dialect is different from Western Arabic, and as the latter form of Arabic, which is the one we know, has hitherto been the best aid to describe Hebrew, what light might be thrown on the text of The Bible – the most important book of ancient times – if we were to learn the eastern dialect of Arabic as well as the western?”

King Frederik approved of the idea. Initially, the plan was to send a researcher, accompanied by a servant, to the Near East, travelling on board a Danish merchant ship. His task was to explore the Yemen and other countries, primarily to make it possible to interpret The Bible with new eyes. Secondly, he was going to carry out studies of geography and natural sciences. As time went by, Michaëlis succeeded in convincing Bernstorff that all these tasks would be too much for one person to carry out. It was agreed that four scientists should go to Constantinople (today’s Istanbul) on board a Danish ship, and from there travel on their own to Egypt, and along The Red Sea to Yemen. The research subjects were Oriental languages, ethnography, medicine, geography, cartography, astronomy, botany, and zoology. An artist should accompany the scientists, besides an orderly to service these five men. This plan roused a stir in European academic circles.

As it turned out, Denmark only held few persons in the natural sciences with the necessary qualifications for the expedition. When corresponding with Bernstorff, Michaëlis as well as Linné praised Pehr Forsskål, Michaëlis because of his knowledge of Hebrew and other Oriental languages, Linné because of his qualifications in natural sciences. Bernstorff was soon convinced that Forsskål should become a member of the expedition. Forsskål’s dispute with ’The Hats’ had made it extremely difficult for him to obtain an academic career in Sweden, so when he, in October 1759, received Bernstorff’s offer to participate in a Danish scientific expedition to the Near East, he grabbed this opportunity with pleasure. His tasks were to collect and describe as many plants and animals as possible, and to note their utilization among the local inhabitants, if any. It was of special importance to find as many as possible of the species mentioned in The Bible. According to instructions from Professor Kratzenstein in Copenhagen, marine-biological studies were to be carried out, of e.g. phosphorescence, fishes, molluscs, and corals.

However, Forsskål did not hide his light under a bushel. To participate in the expedition, he demanded a Danish professorship. He also demanded to become the leader of the expedition – a title, to which von Haven considered himself the obvious choice. Because of these two learned gentlemen’s dispute, Bernstorff chose to make all five members of the expedition equal – something which was unheard of in those days. Forsskål also demanded that when the expedition had been successfully carried out, he was to receive pension from the Danish government, and that he could reside anywhere in Europe. It must have taken Bernstorff some swallowing to accept this demand, but it seems that he was hard up for suitable scientists. Forsskål was a great admirer of Linné, so he applied for permission to send duplicates of collected plants and animals to Uppsala. This was flatly denied, referring to the fact that this was a Danish expedition, and Denmark alone should benefit from the achieved results. All collections were to be sent directly to Copenhagen, from where any duplicates later could be sent to Linné or other scientists in Europe. Forsskål was furious, but accepted this order. Later, however, he started sending letters to Uppsala, containing a system of numbers that only he and Linné knew. In this way, his mentor could obtain descriptions, getting around the Danish bönåser (dabblers) – referring to his employers in Copenhagen. His criticism of Kratzenstein was completely unreasonable, as his marine-biological instructions were indeed far ahead of their time.

As geographer and cartographer on the expedition, Michaëlis recommended a German, Carsten Niebuhr. His primary task was to determine latitude and longitude in localities, visited by the expedition, and to produce maps from these measurements. Furthermore, he was supposed to research in climate and human population issues. He made a good impression on Bernstorff, and as the latter had had a number of bad experiences with von Haven, who, among other incidents, had squandered the king’s money during his stay in Italy, Bernstorff made Niebuhr the economist of the expedition – which made von Haven furious. Niebuhr was younger than the other members, and when he, like von Haven and Forsskål, was offered a professorship, he humbly declined. Instead he got the title of engineer-lieutenant (corresponding to today’s surveyor).

Danish Christian Carl Kramer’s task was to research scientific and everyday medical treatment in the Arabian countries. Furthermore, he had to assist Forsskål during his collections. Kramer’s knowledge was limited, and Forsskål doubted his competence. Instead, he suggested a disciple of Linné, Johann Peter Falck. Forsskål wasn’t exactly diplomatic, and his impetuous behaviour caused Bernstorff to decline his suggestion. Furthermore, he didn’t want the expedition to hold more Swedes than Danes.

The primary task for German artist Georg Wilhelm Baurenfeind was to draw plants and animals, which were too fragile to conserve (e.g. medusa). Furthermore, he was supposed to illustrate architecture, people, and other subjects, which the other members of the expedition found interesting.

The servant was a Swedish dragoon, named Berggren. His knowledge of horses was beneficial to the expedition in Yemen, where he cured one of Emir Bahr’s horses. Apart from that, nothing is known about him.

That winter was characterized by repeated strong gales from north-west, and each time the ship tried to round the northern tip of Jutland, Skagen, it had to return to the town of Elsinore. As von Haven suffered much from seasickness and other agonies on board, he applied for permission to go overland to Marseilles, which was granted. In Marseilles, he would again join the party. On March 10, Grønland once again left Elsinore, and this time it passed Skagen without problems. However, a strong southerly gale now blew the ship all the way up into Icelandic waters – after which it was dead calm for days. Despite all these delays, Forsskål and Niebuhr were full of optimism and didn’t waste their time. Niebuhr practiced locating positions, using his so-called astrolabium, while Forsskål caught sea creatures in a net through the gun ports. He tried to solve the mystery of phosphorescence. By sieving sea water through ever finer cloth, he was able to conclude that the water finally stopped phosphorizing – which meant that the light did not stem from the water itself, but from a living organism in it.

Eventually, Grønland rounded the Rock of Gibraltar, reaching Marseille on May 13. Forsskål went on several botanical collecting trips around the city, and he had time to visit colleagues in Montpellier. Now von Haven had rejoined the party, and during a banquet on board the ship it quickly became obvious that the composition of the expedition members was very unfavourable. During the banquet, various subjects were discussed, among these the Swedes’ elected heir to the throne. Von Haven’s pronounced lack of diplomacy caused him to insult the Swedish chief court official, Tessin. Forsskål retorted, and the quarrel between the two eventually caused von Haven to fling out these pithy words: ”Kiss my arse!” From this day there was cold air between the two learned gentlemen.

On several occasions during the journey across The Mediterranean, Grønland’s crew made preparations to confront English war ships who demanded to inspect the Danish merchant ships, which was refused by the captain. However, direct actions of war were avoided. On June 5, enemy ships were spotted in the distance, and on June 6, the crew on Grønland was busy, preparing defence of the ships. While this took place, Niebuhr calmly stood on deck, using his astrolabium and his telescope to observe and describe a Venus Passage. He was complaining, however, that the ship was shaking too much to make precise observations.

The ships called at the port of Malta June 14-20. Here, Forsskål’s and Niebuhr’s field work started in earnest – almost half a year after the start of the expedition. Forsskål made a list of encountered fossils, 11 molluscs and 3 sea urchins. He does not mention the highly interesting sub-fossils of mammals, e.g. dwarf elephants and hippos, which can be found among the rocks on Malta – presumably he didn’t encounter them. His Florula Insulæ Melitæ includes 78 wild and 9 cultivated plant species from the island, of which he is still author of the genus Pteranthus, and of seven species: Pteranthus dichotomus, Urtica dubia, Coronopus squamatus, Orobanche crenata, Halophila stipulacea, Vulpea fasciculate, and Polypogon semiverticulatus. Following a visit to the San Giovanni Church in Valletta, Forsskål complained that a relic in this church, which is supposed to be a thorn from the Crown of Thorns of Christ, could not stem from Rhamnus spinosa (today named Paliurus spina-christi), and, therefore, had to be a forgery.

In the beginning of September, Niebuhr had almost recovered, and the members left Constantinople on board a Turkish ship, which brought female slaves to Alexandria. Von Gähler had advised them to wear Oriental dress, as he thought this would help them to carry out their work, unchallenged by the locals. On board, Forsskål caught animals in the sea water through a port-hole, and his activities were noticed by some slave girls, who were accommodated in the cabin above. Forsskål had fun, exchanging sweets and fruit with the young ladies.

As it turned out, the honourable von Haven had taken his defeat to Forsskål so seriously that he considered poisoning him and take over leadership of the expedition. In Constantinople, he bought enough arsenic to poison an army. However, Kramer was present and noticed the purchase, and later he referred the incident to the other members. They were deeply alarmed, writing a letter to Bernstorff, in which they urged him to dismiss von Haven. The answer took many months to arrive, but was very clear: According to the royal instructions, the entire party must stay together, and disagreements had to be solved with tolerance. Supposedly, von Haven’s purchase was an act of desperation, as he had several opportunities to poison the other members, which, however, did not happen.

Collecting around Cairo was not without risk, and on several occasions, Forsskål was attacked by robbers. His guide suggested that he should stay in the city, while the guide and his assistants, for a small fee, would bring plants and animals to Forsskål, making it possible for him to study and describe them at his leisure. This arrangement worked to everyone’s satisfaction. In town, Forsskål visited Greek apothecaries to describe which plants, animals, and minerals their medicine stemmed from. He collected information about 565 types of medicine, noting their name in Latin as well as in Arabic, but unfortunately not always their utilization.

While Niebuhr and von Haven travelled to the Sinai Peninsula to visit Jebel el Mokateb and the Santa Catarina Monastery, Forsskål remained in Suez with Kramer to nurse Baurenfeind, who was ill. In this way, he managed to accompany von Haven, whom he detested and despised. However, he later regretted his decision, as time went by, and he began to get bored.

 

After a voyage of 20 days, the boat anchored at the port of Djidda. In this town, the party had to wait until December 13, before they could continue their journey south, travelling on board a smaller boat, a so-called tarrad. For once, it seems that Forsskål didn’t make any collections, but it must be admitted that he had already sent numerous collections to Copenhagen. Some speculate that he suffered from homesickness in Djidda.

Two weeks later, the party arrived at the port of Al Luhayyah (Lohaja), northern Yemen. Here they encountered widespread hospitality, and for all of them the happiest time of the entire journey occurred. Forsskål, who was a linguistic genius, learned the local dialect in no time, and for weeks he and Niebuhr rode on donkeys from one friendly village to another in the Coffee Mountains, stretching north-south parallel to the coast of Yemen, some distance inland. In a crumbling house, near the town of Bayt al Faqih, Forsskål studied termites, which he had not encountered before.

 

In Mocha, their troubles started in earnest. The Turkish governor of this city was very suspicious of these foreigners, and he demanded them to open their boxes, containing their collections. During this operation, part of the content was destroyed, and the cask with alcohol, used by Forsskål to conserve his collected animals, broke. The Arabs were furious that these infidels brought the forbidden fluid into their city, and the party ended up paying 50 Ducates as a bribe to get their boxes back.

Von Haven went from bad to worse, and he succumbed to his illness on May 25. By now, Forsskål was desperate, and after von Haven’s funeral, the party left Mocha as quickly as possible. On June 9, they travelled inland, and despite the difficult conditions, Forsskål continued to carry out his botanical collections. In the town of Torba, his Arab donkey driver committed burglary in the local mosque. Forsskål managed to prevent the donkey from entering the mosque, ”which would have been the only instance in the entire Muslim World History.” Again, his fluent Arabic carried the expedition unscathed past this incident.

Slowly, Niebuhr’s condition improved. Forsskål wished to climb a mountain, Jabal Saber, which, at 3,007 metres altitude, has a very interesting flora, but he had huge difficulties obtaning permission to do it. However, his plans were cancelled, as he, on June 28, suddenly broke down with a high fever. The other members of the party tied him to a dromedary, and, suffering tremendous hardships, they arrived at the town of Yarim (Jerim) on July 5. Here, the mob threw stones at them, and only by paying a huge sum they succeeded in renting a house, in which they could nurse Forsskål. His condition worsened, and on July 11, 1763, he succumbed to the fever. With great difficulty, Niebuhr managed to obtain a place to bury him, but shortly after the burial, the grave was plundered, and today the location of Forsskål’s grave is unknown.

 

While in Bombay, Niebuhr made an excursion to a famous Hindu temple on the island of Elephanta, in which a marvellous statue, called Trimurti, or Mahesamurti, shows the god Shiva’s three aspects: the destructive one, called Bhairava, the preserving one, and the feminine one, Shakti, locally called Vamadeva. He also visited Gujarat, before, in December 1764, he travelled by ship from Bombay to Mascat, Oman. From here, he was able to go to Bushire in Iran, and in the spring he spent a month in the ruined city of Persepolis, copying the numerous cuneiform writings on the pillars. Then, joining caravans, he continued overland to Baghdad and Mosul in Iraq, and on to Halep (Aleppo), Syria. In 1766, he made two side trips to Cyprus and the Palestine, before travelling through Turkey to Constantinople. Here he was housed by von Gähler, who had long thought him dead. Finally, Niebuhr rode overland across Eastern Europe, reaching Copenhagen on November 20, 1767, almost seven years after the start of the expedition.

Undeterred by these events, Niebuhr now arranged Forsskål’s zoological and botanical collections and notes. The herbarium alone comprised about 1750 sheets (more than 2000, if you include algae). When nobody showed the slightest interest in publishing the material, Niebuhr himself published it in 1775 and 1776, in three volumes. The zoological collections are described in a volume, named Descriptiones Animalium Avium, Amphibiorum, Piscium, Insectorum, Vermium; quæ in itinere orientali observavit Petrus Forskål, while the botanical results are presented in a volume, named Flora Ægyptiaco-Arabica sive descriptiones Plantarum quas per Ægyptum Inferiorem et Arabiam Felicem, detexit, illustravit Petrus Forskål.

The third volume, Icones rerum naturalium, quæ in itinere orientali dipingi curavit Petrus Forskål, contains 43 of Baurenfeind’s illustrations from the expedition, namely 20 plant species, one bird, and the rest marine animals, of which the major part were new to science. The text in this volume was supplied by a botanist, Johan Zoëga, who presumably also assisted Niebuhr editing the other two volumes.

His most important zoological effort, however, was in fishes and molluscs. No less than 151 species of fish were described during the expedition. Forsskål invented a unique method to conserve the collected fishes, so that they wouldn’t rot. He simple cut open the fish, removed guts, meat, and most of the bones, after which he placed the skin, including the head, tail, fins, and sometimes part of the vertebra, in the strong sunshine, under pressure. After being dried, the fishes could be kept between sheets, just like pressed plants. 99 skins from The Red Sea, belonging to 60 species, are still present in the Zoological Museum of Copenhagen. Popularly, this collection is called ’Forsskål’s Fish Herbarium’. Today, 52 of the species still carry Forsskål’s name as author, but 48 of these, however, have been moved to other genera. 44 species from The Red Sea were named, using Arabic terms, of these 42 specific names and two genera, Abudefduf and Siganus. In Arabic, abu means ‘father’ and def ‘side’, while duf is a plural appendix, expressing something which is intense. Thus, Abudefduf means ‘the father (i.e. the head) of prominent sides’. The body of several species in this genus is heavily striped.

The term vermium in the title of the book encompasses numerous animal groups, which, in those days, were considered to be related to each other: molluscs without shell or skeleton, molluscs with shell, molluscs with a ‘soft’ skeleton, e.g. sea salps and coelenterates, and corals. Within these groups, Forsskål described numerous new species. He caught the drifting gilled gastropod Ianthina, and described the development of the larvae of this group, which was hitherto unknown. He discovered a new group of keeled marine gastropods, which are pelagic, and an entirely new group of animals, the sea salps, of which he described no less than 10 species. He also described numerous new medusa and no less than 26 species of corals.

Among arthropods, such as spiders, insects, and crustaceans, Forsskål described 62 species, among these a locust, and a species of gall wasp, which plays an important role in the pollination and ripening of the fig fruit. 53 species were briefly mentioned.

From the described plants, Forsskål collected no less than six sets of seeds. French botanist Antoine Banal had given him the idea to send seeds to six important universities in Europe: Copenhagen, Uppsala, London, Paris, Göttingen, and Montpellier. In this cunning way, his mentor Linné could obtain, if not the plant itself, then at least its seeds – and, what was important, with Bernstorff’s acceptance.

During his long stay in Lower Egypt, Forsskål acquired a thorough knowledge of the adaptation of the plant species as regards the annual alternation between dry season and rainy season. He was the originator of several completely new theories. In his opinion, the flower is a modified shoot, in which the petals are modified leaves – a theory which the poet Johann Goethe was accredited with many years later. Furthermore, Forsskål was a pioneer in plant geography. He drew the conclusion that a geographical area can be characterized by its composition of plant species. Again, another person was accredited with this new theory, namely Alexander von Humboldt, in 1805.

Linné had urged his disciple to make a special effort to find the famous Mecca balsam tree of The Bible, which was unknown in those days. Today, we know that Mecca balsam, as well as myrrh, both are resin from trees of the genus Commiphora, of the torchwood family (Burseraceae). Mecca balsam is from Commiphora gileadensis (syn. C. opobalsamum), which grows wild in mountains of southern Arabia, while myrrh is from Commiphora myrrha (syn. C. molmol), which grows wild in Somalia and Ethiopia. These two products, and resin from Boswellia sacra, which is utilized as incense, were very important trading items during more than 3,500 years, and numerous caravans travelled from Southern Arabia to the coasts of The Mediterranean.

In April 1763, Forsskål and Niebuhr were working in the Coffee Mountains, when Forsskål, near the village Öude (Uday), noticed something glinting in a flowering tree. As it turned out, the glinting was caused by the reflection of sunshine on resin on the tree. After a short inspection, Forsskål realized that he had found the Mecca balsam tree. As quickly as possible he sent a letter to Linné, containing a flowering twig from the tree. The letter, however, didn’t reach Sweden until September 1764. Naturally, the flowers had withered by then, but nevertheless Linné, from the twig, and from Forsskål’s enclosed notes, was able to describe the species, naming it Amyris opobalsamum.

In Yemen, Forsskål described many new plant species, e.g. a very low member of the oleander family, with a very fat trunk, which he named Nerium obesum (today called Adenium obesum), a member of the arum family with a yellow spathe, Arum flavum (today Arisaema flavum), a species of fig, Ficus palmata, two legumes, Lathyrus spectabilis (today Clitoria ternatea) and Indigofera spicata, a species of primrose, Primula verticillata, and two orchids, Orchis aphylla (today Habenaria aphylla) and Orchis flava (today Eulophia streptopetala var. rueppelii).

In Yemen, like in Egypt, Forsskål made notes about the utilization of plant species as traditional medicine etc. A single example is a species of the birthwort family, Aristolochia sempervirens (today A. bracteolata), about which he said that the crushed leaves were used as a remedy to heal wounds, and to treat snake bites. Even today, this species is a remedy in Yemen to treat snake bites.

During the 1770s, there were plans to publish Forsskål’s diary, but they were not carried out. As a matter of fact, for almost 200 years it was believed that the diary had disappeared, until a copy was found in the university library in the town of Kiel, northern Germany. It was published in Swedish in 1950, titled ‘Journey to Happy Arabia. The diary of Petrus Forsskål 1761-1763’.

Niebuhr’s diary and other notes were published in German in three volumes, in 1774, 1778, and 1837, respectively, titled ‘Description of Arabia and other nearby countries’. Niebuhr’s greatest achievement was in cartography. For the first time, Malta was precisely placed on the Mediterranean map. His map of The Red Sea was so detailed that European ships, by following it, without problems could navigate waters, filled with reefs, all the way up to Suez. His copies of the cuneiform writings on the pillars of Persepolis were so precise that they provided a basis for the deciphering of the script in 1802.

Von Haven’s notes are kept in The Royal Library in Copenhagen, comprising two volumes. One is a travelogue, the other contains a list of acquired manuscripts, copies of inscriptions, and two short lists of translated words, one Arabic-Danish and one Arabic-Italian (the latter from his stay in Rome). Prior to the expedition, the library’s collection of Near-Oriental manuscripts consisted of rather accidental purchases and gifts, but with von Haven’s competent purchases, the library was now in a much stronger position in this field. His diary was published in Danish in 2005, titled ‘The loss of my health. Frederik Christian von Haven’s travelogue from The Arabian Journey 1760-1763’.

Baurenfeind’s drawings were precise and realistic.

Forsskål was utterly cool to hardships and dangers, and during his research trips in Egypt he was confronted by robbers on several occasions. He also assisted Niebuhr, when the latter was making measurements of the Giza Pyramids, but here his stubbornness caused quite a few problems. A young Bedouin offered to be their guide, which was declined by Forsskål. This made the young man so angry that he knocked Forsskål’s turban off his head. However, Forsskål did not react to this, but calmly said to the young Bedouin’s two companions: ”You Bedouins, among your fellow-countrymen it is believed that the Franks (Europeans) at any time are safe under your protection. I have travelled among your fellow-countrymen. If you allow your companion to rob me, I am going to tell my fellow-countrymen that among you you find neither faithfulness or faith.”

This torrent of words had the effect that the young Bedouin’s companions did not allow him to rob Forsskål. Instead, he turned towards Niebuhr and tried to grab his precious astrolabium. This made the quiet German so upset that he pulled at the Bedouin’s clothes, which caused him to tumble off his horse. The young man got so furious that he pulled his pistol and pointed it at Niebuhr’s chest. He writes: ”I must admit that I thought I was going to die. But, presumably, the pistol was not loaded.” The Bedouin was calmed by his companions, and in the end he accepted a small sum as compensation from Niebuhr.

Forsskål showed great versatility in his knowledge and interests. Likewise, his nature was indeed complex. At most times, he was friendly and amiable towards the locals, as well as towards persons whom he respected, such as Niebuhr, who possessed the same virtues as himself. On the other side, he could be extremely arrogant and condescending towards persons, who showed signs of weakness, e.g. the lazy Kramer, and the indolent and timid von Haven, who spoke only a little Arabic and, furthermore, didn’t like the Arabs and their way of life. This passage from Forsskål’s letter to Linné, following von Haven’s death in Mocha, shows his implacability after his controversies with the deceased, coupled with an ample dose of cynicism: “One of our party, Professor von Haven, died here on May 25, and his departure made travelling so much easier for the rest of us. His disposition was rather troublesome.”

Forsskål had asked Linné to name a plant after him. Linné chose a plant of the nettle family, which Forsskål had named Caidbeja after the town of Caid Bey, where he first found it. Linné renamed it Forsskaolea tenacissima, and his description also contained the adjectives hispida, adhærens, and uncinata. These four words mean something like stubborn, stiff, obstinate, and bent. When Niebuhr read the description, he was infuriated, regarding it as a scorn towards the deceased. However, this was hardly Linné’s intention, as he regarded Forsskål as one of his most gifted disciples, but, presumably, he found his characterization of the temperamental and somewhat obstinate Forsskål very apt. In reality, the word tenacissima can also be translated as determined or energetic!

Niebuhr characterized his friend as follows: “Forsskål was the most learned person of our party, and had he returned home alive, he would have been the most learned person in all of Europe. He was hard-working, and he despised all dangers, hardships, and renunciations. His shortcomings were his fondness of discussion, his willfulness, and his hot temper.”