Haplophyllum patavinum (L.) G. Don fil. (Paduan rue)

Classification, Distribution, and Importance of the Plant

The genus Haplophyllum belongs to the family Rutaceae. More than 70 species, growing from the Mediterranean region to eastern Siberia (most of them in western and central Asia), are assigned to this genus. Only eight species can be found in Europe (); H. patavinum (L.) G. Don fil. is the only species occurring in Italy.

H. patavinum was first collected on the Euganean Hills (NE Italy), probably in 1722, by the Italian botanist Micheli, who described it as Pseudo-Ruta patavina (Micheli 1729) and stressed the differences from the genus Ruta (“plantae genus a Ruta diversum”). This species, described by Zanichelli (1730) as Pseudoruta Micheli, was then included by Linnaeus (1753) in the genus Ruta (Ruta patavina L.). De Jussieu (1825) split the genus Ruta into two genera, Ruta and Aplophyllum; the plant species from the Euganean Hills was assigned to the latter genus by Don (1831). Spach (1849) changed Aplophyllum into Haplophyllum.

At present, there is general agreement regarding Haplophyllum as a genus distinct from Ruta, on the basis of morphological characters and chemical evidence.

H. patavinum () belongs to the section Oligoon of the genus Haplophyllum (dehiscent fruit with five carpels and two ovules in each loculus) according to Vvedensky (1949). It is a perennial herb with yellow flowers in dense cymose inflorescences; leaves crowded, basal leaves simple, middle leaves 3-sect to the base, uppermost leaves linear, simple, or 3-sect. The leaf morphology and also the leaf width are very varied.

Two varieties of H. patavinum were described. The variety albanicum of Baldacci (1901) later described as a separate species, H. albanicum (Bald.) Bornm., is now regarded as a synonym of H. boissieranum Vis. & Pancic. According to Beguinot (1905), the wide variability in leaf width and the occurrence of many intermediate forms do not support the variety angustifolia (Ruta patavina L. var. angustifolia Nob.).

The chromosome number of H. patavinum is 2n = 18.

H. patavinum has a discontinuous distribution with a wide illyrian range extending from Albania to Slovenia and a punctiform relict disjointed range on the Euganean Hills. Further information and details on distribution of the species can be found in Dolcher (1957). The plant grows in open habitats on well-drained calcareous soils (dry and sunny slopes, edges of the roads, uncultivated stony fields).

In the punctiform relict Euganean range, H. patavinum forms endangered and highly unstable populations, which are facing slow extinction as the result of habitat modification by man’s activities and the peculiar propagation features of the species. The species has been included in the Red Book of Italian threatened species.

To the authors’ knowledge, no use of H. patavinum in folk medicine is reported and no phytochemical investigation had been previously undertaken. Nevertheless, this species is worthy of investigation, since biologically active natural substances of potential pharmaceutical interest are known to occur in the genus Haplophyllum, namely coumarin compounds, quinoline and other types of alkaloids, and lignans.

Another species, H. tuberculatum (Forssk.) A. Juss., is used in Iraqi and Saudi Arabian folk medicine for a variety of ailments including malaria, rheumatism, gynecological troubles, as an aphrodisiac, and as a cure for scorpion stings. Some of its chemical constituents have antimicrobial and antimalarial activities (); moreover, plant extracts may provide a potential alternative for insect control.

The small size of H. patavinum populations and the consequent scarcity of plant biomass available in the natural habitat had hitherto hindered systematic chemical investigations. Therefore, in vitro culture of this species has been undertaken to obtain additional plant material and, in the meantime, to set up non-conventional practices for plant propagation.

Conventional Propagation

Natural propagation of H. patavinum is mainly vegetative, by shoots arising from the rhizome. Therefore, agricultural practices such as deep plowing lead to the disappearance of the plant. In the natural habitat, the production of viable seeds is very scarce, since frequent embryo abortion at different developmental stages was observed.

Slightly greater amounts of viable seeds are produced by specimens transplanted to different soil (unfortunately, the transplanted specimens do not survive for long), which supports the hypothesis put forward by Cappelletti (1929) of sterility of mycotic origin. In plants of H. patavinum cultivated in the Botanical Garden of Paduva, vegetative propagation occurs frequently, but only one seedling was observed.

Haplophyllum patavinum (L.) G. Don fil. (Paduan rue): Conclusion

In vitro culture of H. patavinum has to be considered as a useful tool for the conservation of this rare and endangered plant. Seed germination, which occurs very rarely under natural conditions, is considerably enhanced in vitro, allowing successful establishment of plants. This fact is particularly important when the very low viable seed production from the native populations in the Euganean Hills is considered. Moreover, seeds are preferred to vegetative material as the source of propagation material because a wider genetic base can be maintained.

H. patavinum can be multiplied in vitro from nodal shoot segments, a protocol which involves regeneration from existing meristems.

In comparison with other Haplophyllum species, H. patavinum is not rich in coumarin compounds in vivo. However, a selected cell strain exhibited in vitro coumarin biogenetic potentialities stronger than in vivo. In fact, new structures, not yet isolated in intact plants, are produced by calli and excreted into the solid medium, from which all the intermediate products of the biogenetic pathway of the angular furocoumarin, have been isolated.

Although other angular furocoumarins have been detected from species of the genus Haplophyllum (), the occurrence of the angular furocoumarins columbianetin and angelicin, and the prenylated coumarin osthenol had not previously reported.

Investigations on the biosynthesis of other classes of metabolites could lead to the detection of other pharmaceutically active compounds, since preliminary unpublished data have shown the production of lignanolide compounds by H. patavinum in vitro.

Selections from the book: “Medicinal and Aromatic Plants X”, (1998).