The Incredible Story of Palo Azul

isaac newton

A long, long, time ago… 

...Shortly after the discovery of America, there was a plethora of wonderful products of the new world brought to Europe. Among them, was a Mexican wood supposed to be efficacious as a diuretic and therefore called “lignum nephricitum” (palo azul)

Even more surprising was its remarkable property of blue fluorescence, which was studied by two scientists that you may have heard... Isaac Newton and Alexander Graham Bell!

That's right, the same giants who established the Theory of Universal Gravitation, the 3 laws of motion, calculus and the inventor of the telephone...were also fascinated by palo azul's fluorescence!

Fluorescence was discovered for the first time in palo azul!

palo azul fluorescence

In fact, the books "Photochemical & Photobiological Sciences" and "Early History of Solution Fluorescence" mention that the phenomenon of fluorescence was discovered for the first time in palo azul!

The first scientist to establish a botanical description of this plant was named Hernandez. This description was very confusing and the full description was never found. Because of this confusion, this plant was lost for 300 years without being identified. And thus, the search for the true lignum nephricitum had begun.


Long story short, after dozens of scientists attempting to search for it and countless mishaps and mistakes, the true source of palo azul, was identified. Finally, we can all take delight in its radiant beauty and enjoy the magical healing benefits that it naturally offers. 

magiktea palo azul logo

Now you see why we called it Magiktea? ;)
Try palo azul and experience the magical fluorescence of the same tea that amazed Isaac Newton and Alexander Bell!

The incredible Story of Palo Azul

isaac newton and alexander graham bell studying palo azul

Hernandez (1576) was the first to establish a botanical description of this plant, which he described under the name “coats, or coati.” He was a physician rather than a naturalist, and many of his descriptions and illustrations of plants tended to be crude and almost unrecognizable.

He was uncertain regarding the plant producing it, stating that it was described to him as a shrub, but he had seen specimens of it exceeding a very large tree. Hernandez’s work never appeared as a whole and for 2 centuries the plant remained unidentified botanically. And thus, the search for the true lignum nephricitum had begun, so get ready for a magical and surprisingly unexpected journey through time. 

To make the story easier to follow, below we have provided bullet points for each different event in the attempt to discover the true lignum nephricitum.

Identifying the True Lignum Nephricitum

• Following the aforementioned scientists who studied this plant, came Caesalpinius (1583) and Caspar Bauhin (1623), who supposed it to be a species of a plant called Fraxinus.

• Next up is John Boeclerus (1745), who believed it to come from a tree called Laburnum, and called it Cytissus mexicanus. 

• Then, Linnaeus, in his Materia medica (1749), added to the confusion by referring to it as Mooring pterygosperma, an East Indian tree, in spite of the fact that it was originally declared to be of Mexican origin.

• Nearly 70 years later, Guibourg, in his Histoire abrégée des drogues (1820), identified it with the West Indian cat’s-claw (Mimosa unguis-cati L.).

• Finally, some progress came from Dr. Leonardia Oliva, Professor of Pharmacology in the University of Guadalajara.  He was the first to indicate its true botanical classification in his Lecciones de Farmacología, where he identified it with Varennes polystachya DC. And just as this revelation came, it was subsequently dismissed by authorities who did not accept his identification….(sigh)…

• So now we’re onto Dr. Fernando Altamirano (1878), who recognized that the identity of the lignum nephricitum of Hernández came from the tree called by the modern Mexicans as palo dulce and referred as Viborquia polystachya Ortega, but he was not aware that the latter was the same as Eysenhardtia amorphoides H.B.K. Because of this mishap, he mistakenly followed another scientist, Alfonso Herrero, in identifying lignum nephricitum as Guilandina mooring.

ortega palo azul eysenhardtia poylstachya

* Here comes an important part! Sargent, in his “Silva of North America,” gave an amended description of the genus Eysenhardtia, in which he for the FIRST TIME established the combination Eysenhardtia polystachya, but he had no idea that this species had anything to do with lignum nephricitum, or that its wood yielded a fluorescent infusion.

• Hanbury had been seeking for lignum nephricitum for years, but had no success. Both Hanbury and Flückinger published their well known “Pharmacographia (1879),” but chose to be silent about lignum nephriticum.

• Coming up is Dragendort, (cool name right?!) who refers to it as a species of Guajacum. However, he was influenced by Ramírez and Aclocer’s “Sinonimia vulgar y científica de las plantas Mexicanas” (1902), and so he referred to a piece of wood in the Paris Exposition which was labeled “cuatl” and identified it as Eysenhardtia amorphoides; but the wood was unaccompanied by botanical material by which it might be identified with certainty.

* Here comes another important part! The last author to investigate the origin of lignum nephircitum is Dr. Hans-Jacob Möller, of Copenhagen, who after an exhaustive study of the wood referred to it as a Mexican tree belonging to the genus Pterocarpus. Dr. Möller carefully examined various woods that were allegedly supposed to be the true lignum nephirticum mexicanum.

Among them were specimens of the wood Eysenhardtia amorphoides, but it reported negative results. He then examined the heartwood of a Philippine species of Pterocarpus, and he found that in water containing lime, it yielded an infusion having the characteristic sky-blue fluorescence of lignum nephritic mexicanum as described by early investigators. He therefore assumes that the mother-plant of lignum nephritic mexicanum, “sought in vain for 300 years by so many investigators, is a Mexican species of Pterocarpus.” 

palo azul eysenhardtia polystachya ortega illustration

Sought in vain for 300 years, and finally found

At last! After 300 years of searching for the true lignum nephriticum of Hernández it was identified……..except that it wasn’t…(sigh). The leaflets of the species of Pterocarpus figured by Möller himself exceed 6 cm. in length by 3.5 cm.

Hernandez described the leaves as “resembling those of Cicer arietinum [chick-pea] but smaller,” and also compared them with the finely divided leaves of the common wild rue, therefore it cannot possibly be identified with any known Mexican species of Pterocarpus. So the search continued.

To further add to the mystery, Hernandez’s original description of lignum nephricitum actually described TWO different species! It is as follows: “They call coati a plant which they describe as a shrub; but I have seen it larger than very large trees; and some call it tlapalezpatli, or blood-red medicine.”

The first, with leaves resembling those of Cicer Arietinum [chick-pea] and with spikes of small longish flowers, is undoubtedly Eysenhardtia polystachya, which never exceeds the size of a small tree. The second is in all probability a species of Pterocarpus, which grow to much larger dimensions than the Eysenhardtia.

Palo azul / Eysenhardtia polystachya, The true source of Lignum nephricitum

The writer of this article (William Edwin Safford) had been seeking the source of lignum nephricitum for years. He examined specimens of Eysenhardia polystachya that he collected in 1907.

The infusion however, gave no evidence of fluorescence in ordinary sunlight and the specimens that he had seen were either shrubs or trees too small to yield wood for the manufacture of bowls and cups. For this reason, he was inclined to agree with Möller in discarding Eysenhardtia as a source of the famous wood.

That was the case until July, 1914, when specimens of a medicinal wood from Mexico were brought to the writer along with herbarium material from the same tree sufficient to identify it. The individual who brought them hadn’t noticed anything about the color of its infusion, but dwelt upon its efficacy as a cure for certain diseases to which fowls are subject in Mexico.

This wood proved to be the famous Eysenhardtia polystachya, commonly known by the modern Mexicans as palo dulce (palo azul), or “sweet wood” The following is the author’s description of Palo Azul’s glow:

palo azul blue fluorescenct color

“A few small chips of the heartwood in ordinary tap water tinged the latter a golden yellow, which soon deepened to orange, and looked like amber when held between the eye and the window. When the glass vial containing the liquid was held against a dark background the liquid glowed with a beautiful peacock blue fluorescence. Placed party in a sunbeam, half of the liquid appeared yellow and the other half blue; and when sunlight was focused upon it by the lens of a common reading glass, the vial appeared to be filled with radiant gold penetrated by a shaft of pure cobalt.”

There was no longer any doubt as to the identity of the wood. It could only be the true lignum nephricitum of Robert Boyle’s experiments; and it was undoubtedly the wood of Eysenhardtia polystachya. 

alexander graham bell

Following this event, the author went to the house of the famed scientist and inventor Alexander Graham Bell on the evening of January 15, 1915 and presented to him the specimens of the wood. The author describes:

“Specimens of the infusions when exhibited by ordinary electric light failed to show fluorescence; but afterwards, when held in the rays of an arc light the liquid glowed with intense blue which illuminated the faces of those standing nearby.”

isaac newton and alexander graham bell studying palo azul

The End!

For the first time in nearly 300 years, the identity of the true lignum nephricitum which Hernández originally described had been established beyond a doubt. Its characteristic fluorescence corresponded accurately with the descriptions that Isaac Newton and Robert Boyle obtained in their experiments about fluorescence.

After dozens of scientists attempting to search for it and countless iterations of inaccurate names, the true source of lignum nephricitum, or Eysenhardtia Polystachya… or palo azul, was identified. Finally, we can all enjoy the most magical tea in the world. 


magiktea palo azul logo