Aristolochia arborea: The Biology and Thread of a Remarkable Rain Forest Tree from Central America

Introduction

Only a very few specimens of this very attractive plant are in cultivation. The specimen at Bonn has been collected at the Botanic Garden Bogor by one of the authors (ROTH). A few specimens have been cultivated in Bogor since the beginning of this century (CAMMERLOHER 1922), and at least one plant has survived until the present day (see VOGEL 1978). There is nothing known about the origin of these plants. A specimen was already fully mature by the time of CAMMERLOHER. Therefore one can assume that this plant specimen belonged to LINDEN´s collection and probably represents type material.

Cuttings of the two plants at Bonn were sent to the Botanic Gardens Berlin, Frankfurt (Palmengarten), Hamburg and Munich. Aristolochia arborea is also in cultivation at the Royal Botanic Gardens Edinburgh, but the origin of this plant is unknown, too (R. KERBY, pers. com.). PFEIFER (1966) reports, that a person called BROADWAY has collected material from cultivated plants in Trinidad.

Due to the fast decline of central American rain forests and the fact that only few documented collections of Aristolochia arborea exist, one can assume that this species is extremely threatened.
 

The taxonomy of Aristolochia arborea

25 francs (~ 1£) (LINDEN 1858). Although this description was not very precise, some of LINDEN´s plants arrived at Kew and were later illustrated in Curtis Botanical Magazine (HOOKER 1862, Fig. 1). This article is therefore the first description in conjunction with that illustration.
 

Fig. 1: Illustration of Aristolochia arborea taken from: Curtis Botanical Magazine.

 

In his revision of the genus Aristolochia from north and central America, PFEIFER (1960) placed A. steyermarkii STANDLEY and A. salvadorensis STANDLEY into the synonymy of A. arborea. Having studied original descriptions of these species and living specimens of A. salvadorensis (obtained by H. W. WELTZ, BG Hamburg) the authors regard these species as clearly distinct. The very few locations of these three species are to be found in South-Mexico, Guatemala and El Salvador.

Based on the results of the systematic study on Aristolochiaceae HUBER (1960, 1985, 1993) divides Aristolochia into several genera. According to his findings A. arborea should be placed into the genus Isotrema, close to Isotrema (Aristolochia) tricaudata.
 

Flower Morphology and Pollination Biology:

Fig. 2: Dense arrangement of flowers at the base of the stem  Fig. 3: Single flower showing the imitation of a small toadstool

Until recently the few specimens of Aristolochia arborea grown at Botanic Gardens were propagated by means of cuttings. Therefore it is most likely that all cultivated plants are clones. There are no reports on any sexual propagation of the species. The reason for this may be found in an phenomenon, not yet understood: The flowers are protogynous. The three stigmatic lobes spread during the female stage and produce a wet stigmatic liquid. This liquid dries out and the stigmatic lobes close firmly together before the flower opens. This mechanism prevents a successful pollination under natural conditions and allows pollination only accidentally. At the time the flowers open, the anthers already shed the pollen. This phenomenon was already observed by CAMMERLOHER (1922), who opened flowers during the female stage and pollinated them artificially. During his research at Bogor BG he noticed that A. arborea produces fruits after self-pollination. However he does not report of seed germination nor on the results on any germinated off-spring.

Aristolochia arborea is a very rare and attractive species. The research conducted by CAMMERLOHER provided the base for hand pollination of the two specimen grown at Bonn BG.
 

Fruit Morphology and See Dispersal

5 to 6 months after pollination the fruits opened from the tip. The fruit splits into 6 parts which roll back, continously releasing approximately 60 seeds. After 10 days the seeds were released and the fruit decomposed totally (Fig. 5). The seeds are arranged in six rows densely packed and are heart-shaped. They are approximately 1 cm long and 0.8 cm wide and are embedded in a massive elaiosom. The elaiosom is twice the size of the seed. The seeds are collected by ants and carried away. Smaller ants carry the seeds away in a highly coordinated manner (Fig. 6).
 

	Abb. 4: Fruit (final size), ca. 15 cm
	Abb. 5: The fruit splits into 6 parts which roll back, continously releasing the seeds.
	Abb. 6: Seed with a massive elaiosom attracting ants

After 4-6 weeks 40% of the seeds germinated. The germinated seedlings are already plants of more than 1.5 m and flower regularly. Although they originated from self- pollination the plants show variability within the population: There are a few plants that do not produce any side shoots as the centre stem grows in height. Other plants branch freely and therefore remain small.

Having produced a nurnber of individuals by means of sexual reproduction one can expect the survival of this species at least under cultivated conditions. Seedlings were send at least to Amsterdam, Missouri, Kew (1995), Meise, Göteborg, Tübingen and Dresden. Hopefully Aristolochia arborea, as one of the most beautiful species in the genus, will not only been seen in Botanical Gardens.
 

Acknowledgements:

Literature:

Zurück zu den bemerkenswerten Pflanzen  back to the Homepage of the Botanical Garden Bonn
Stand 08. Oktober 1998, URL: http://www.botanik.uni-bonn.de/botgart/arisarbe.htm
Wolfram Lobin
© Botanischer Garten Bonn 1998