Pitaya

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Figure 1 – Flower of H. undatus. Photo by  O. Tellez-Valdes, FESI-UNAM.

Taxonomy and Nomenclature

Family. Cactaceae

Synonyms.Cereus tricostatus Rol.-Goss., C. trigonus var. guatemalensis Eichlam, C. undatus Pfeiff., C.undulatus D.Dietr., Hylocereus guatemalensis (Eichlam) Britton & Rose, H.tricostatus (Rol.-Goss.) Britton & Rose

Vernacular / common names. Dragon fruit, queen of the night (English); pitahaya, pitaya (indigenous names).

Plant Description

Life Form. Epiphytic cactus.

Plant. Climbing, scrambling or shrubby; stems 3–6 cm wide, ribs 3, margins wavy, aerial roots present.

Leaves. Reduced to spines, 1–3(–5) per areole, spines 2–4 mm long, c. 1 mm wide at base, conical, straight to slightly curved, whitish to grey.

Flowers. Spectacular, funnel-shaped, opening at night, white, 26–30(–35) cm long, 15–20 cm in diameter (Figure 1) [1,2].

Fruits and Seeds

Fruits are purple, with a white flesh, 10–12 x c. 7 cm (Figure 2). Seeds are black, c. 2.8 x c. 2.5 mm  (Figure 3) [2].

Flowering and fruiting. Flowers between May and August; fruits from July to September [2].


Figure 2 – Longitudinal section of the fruit with seeds. Photo by O. Tellez-Valdez.



Figure 3 – External views (top) and longitudinal sections (bottom) of the seeds. Photos by P. Gomez-Barreiro, RBG Kew.

Distribution

The native range of this species is not known. Hylocereus undatus has long been in cultivation; escapes from cultivation have become widely naturalised. It is found in USA and Mexico, through Central America to South America, and throughout the Caribbean region, from sea level to 2,750 m a.s.l. [1,2,8]. It is also naturalised in parts of tropical Asia, Australia, and on several Pacific Ocean islands, and can be invasive (e.g. in Florida and in parts of Australia and South Africa).

Habitat

Deciduous dry forests, xerophilous scrub and cultivated in gardens [2].

Uses

Hylocereus undatus is commercially grown for its edible fruits. In Mexico, the fruits are harvested from naturalised and cultivated plants. In traditional medicine, the flowers are used to prepare tea to treat cardiovascular conditions. The stems are used to treat common cold [2]. Widely grown by cactus enthusiasts and planted as an ornamental [1,2], H. undatus is also used as a rootstock for grafting other species of cacti.

Known Hazards and Safety

Care should be taken when handling the plant as the spines are sharp.

Conservation Status

Widespread and assessed as Data Deficient (DD) according to IUCN Red List criteria because the native distribution is unknown [8]. Hylocereus undatus is not included in the national list of protected species in Mexico [6].

Seed Conservation

Harvesting. Fruits are harvested by hand using a long pole. 

Processing and handling. Harvested fruits should be kept in paper or cotton bags until they are delivered to the seed bank, where they can be cut open with a knife to extract the seeds from the pulp. The seeds should then be washed under tap water and dried at room temperature, after which they can be passed through a sieve or cleaned with pressurised air to separate the seeds from the dried pulp.

Storage and viability. X-ray analysis carried out on seed lots stored at the MSB revealed a high percentage of filled seeds (c. 100%). Seeds of this species are reported to be desiccation tolerant [10].

Propagation

Seeds

Dormancy and pre-treatments: High germination percentages have been achieved on seeds stored at the MSB without any pre-treatments. Seeds of this species do not exhibit dormancy [4]. However, further studies are needed to confirm the lack of any class of seed dormancy. Prior to sowing at the San Rafael, Coxcatlán nursery, seeds were surface sterilised using 4% sodium hypochlorite for 30 minutes.

Germination, sowing and planting: Seed lots stored at the MSB germinated to c. 80–90% when incubated in the light (8 or 12 hours of light per day) at constant temperatures (21–25 degrees C), whereas c. 70% germinated at higher temperatures (i.e. 30 degrees C).

Vegetative Propagation. Readily establishes from stem cuttings. In studies carried out by FESI-UNAM staff, cuttings were treated with three different concentrations (10, 100 and 1,000 ppm) of indole-3-acetyl-p-nitrophenyl ester (IAP) and planted in plastic bags. Rooting success and the number of roots per plant were evaluated after two weeks. Rooted cuttings were transplanted to plastic bags using ‘tezontle’ (a porous, volcanic gravel) as the substrate. The most successful treatment was the application of 10 ppm IAP (resulting in 100% of cuttings rooting). Commercially propagated from both seeds and cuttings [7]. A protocol for in vitro propagation has been published [9].

Trade

A commercial fruit crop (grown in several regions of the New World, tropical Asia and warmer parts of Europe) that is internationally traded. Locally, in Zapotitlán, Salinas (Puebla), there are organisations concerned with developing the economic potential of the species [3]. International trade of plant material is regulated by CITES (listed on Appendix II) [5].

More from Wild Plants for a Sustainable Future:

 
Cover courtesy of The Royal Botanic Garden, Kew


Excerpted with permission from Wild Plants for a Sustainable Future: 110  Multipurpose Species, editedby Tiziana Ulian, Cesar Flores, Rafael Lira, Avhatakali Mamatsharaga, Kebadire K. Mogotsi, Patrick Muthika(t), Samodino Ngwako, Desterio O. Nyamongo, William Omondi, Abdoul K. Sanogo, Sidi Sanogo and Efisio Mattana. Published by the Royal Botanic Gardens, Kew, and distributed by University of Chicago Press, 2019.  © The Board of Trustees of the Royal Botanic Gardens, Kew 

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