Pitcher plant (Nepenthes holdenii)

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Pitcher plant fact file

• Description
• Biology
• Range
• Habitat
• Status
• Threats
• Conservation
• Find out more
• Glossary
• References
• Print factsheet

Pitcher plant description

The magnificent Nepenthes holdenii belongs to a closely related group of carnivorous Indochinese pitcher plants that are set apart from other pitcher plant species by their ability to flower without having first grown their pitchers ⁽¹⁾. This species was first discovered in 2006 by botanist and photographer Jeremy Holden, and formally described in 2010 ⁽⁴⁾.

As in other pitcher plants, Nepenthes holdenii’s vase-shaped ‘pitchers’ are modified leaves that are deadly insect traps ⁽⁵⁾. The pitchers grow from tendrils projecting from a leathery leaf tip, and have a ‘lid’ and an opening at the top, the surrounding part of which is known as the peristome. Each year Nepenthes holdenii grows a circular arrangement of leaves at its base, from which climbing shoots grow to around five metres tall. Like other members of the Indochinese pitcher plants, Nepenthes holdenii develops swollen, irregular roots that are up to 25 centimetres thick ⁽¹⁾.

The oval-shaped lower pitchers of Nepenthes holdenii grow near the ground and are red, brown or purple on the outer surface, with weak purple markings. Occasionally they are green with a red peristome, although this colouration is rare. The inside surface is creamy-white to yellowish green, and occasionally spotted purple. Two fringed ‘wings’, approximately 15 millimetres wide, run down the outer surface from the peristome to the bottom of the pitcher. The upper pitchers of Nepenthes holdenii are similar in shape but grow higher up on the plant and tend to become narrower towards the bottom. They are usually completely green, with or without a reddish-orange peristome, or may be brown, pink or red with faint purple spots and a reddish-orange peristome. The inside of an upper pitcher is creamy-white to yellowish-green and very occasionally spotted purple ⁽¹⁾.

Nepenthes holdenii can be distinguished from all other closely related Indochinese pitcher plants by the unique growth of its inflorescence. Both the male and female flowers grow in small clusters, but on separate plants. Small stems grow from the main stem of the raceme, with each small stem dividing into two, bearing one flower on each branch ⁽¹⁾.

Size

Lower pitcher height: 13 - 20 cm ⁽¹⁾

Upper pitcher height: c. 25 cm ⁽¹⁾

Lower pitcher width: 4 - 6 cm ⁽¹⁾

Upper pitcher width: c. 6 cm ⁽¹⁾

Pitcher plant biology

Like other pitcher plants, Nepenthes holdenii is carnivorous, its pitchers filled with acidic digestive juices able to break down insects that unwittingly fall into them ⁽³⁾. The carnivorous nature of this species is an adaptation that allows it to survive in nutrient-poor soils, as it gains nutrients from whatever falls into its pitchers ⁽⁵⁾.

Nepenthes holdenii is also fire-resistant, occurring in an area prone to regular fires. This species is able to avoid destruction by fire by growing large, swollen roots underground that produce a new pitcher-bearing vine once the fire has passed ⁽⁵⁾. These underground swellings, or tubers, are able to store enough water and nutrients for the plant to survive extended periods of drought as well as the frequent fires. Another survival technique of Nepenthes holdenii is its cessation of leaf, flower and pitcher production during the dry season. Individuals growing in particularly exposed conditions will enter a period of dormancy during this time ⁽¹⁾.

Pitcher plant range

Nepenthes holdenii is known only from the Cardamom Mountain Range in western Cambodia, within the remote Pursat Province ⁽¹⁾. 

Pitcher plant habitat

The first populations of Nepenthes holdenii were found on two neighbouring peaks of the Cardamom Mountains. The two sites are situated in a transitional habitat zone between lowland evergreen forest and low montane evergreen forest, between elevations of 600 and 800 metres ⁽¹⁾.

Nepenthes holdenii occurs on steep ridges where it is partly or fully exposed to sunlight, growing in peaty soil covered with leaf litter. Average rainfall in the Cardamom Range where this species exists is 3,000 millimetres per year, and the region has an annual dry season that lasts for more than four months. Even during the wet season, Nepenthes holdenii’s habitat can be extremely dry ⁽¹⁾. 

Pitcher plant status

Nepenthes holdenii is not yet classified on the IUCN Red List, but all Nepenthes species are listed on Appendix II of CITES ^{(2) (3)}.

Pitcher plant threats

The main threat to tropical pitcher plants is thought to be habitat destruction. However, species are also increasingly at risk from collection for illegal trade as populations become smaller. Illegal trade in Nepenthes species is known to be high ⁽³⁾, and given the uniqueness of Nepenthes holdenii and its few known locations, it is possible that illegal trade could also affect this species.

Pursat is one of Cambodia’s most remote provinces, and it is heavily mined. Both these factors could inhibit attempts to conduct necessary additional research on Nepenthes holdenii ⁽¹⁾.

Pitcher plant conservation

All Nepenthes species are listed on Appendix II of the Convention on the International Trade in Endangered Species (CITES), meaning that any international trade of these species should be carefully controlled and monitored ⁽³⁾. Nepenthes holdenii is not in cultivation as the plants were either too old or too young to harvest at the time this species was discovered ⁽⁶⁾.

In 2011 a new population of Nepenthes holdenii was discovered on an unrelated expedition to the Cardamom Mountains in Cambodia. This is good news for the species ⁽⁶⁾, and further study may reveal if Nepenthes holdenii grows at other locations in the region ⁽¹⁾. 

Find out more

Find out more about Nepenthes holdenii:

• A garden’s chronicle blog - Nepenthes holdenii:
  http://carnivorousockhom.blogspot.co.uk/2010/10/nepenthes-holdenii.html
• Fauna and Flora International - New species of carnivorous plant discovered in Cambodia:
  http://www.fauna-flora.org/news/new-species-of-carnivorous-plant-discovered-in-cambodia/
• Associazione Italiana Piante Carnivore - 2010: New species of carnivorous plants:
  http://www.aipcnet.eu/Carnivorous_docs/New_species_2010_Mara_Guerini.pdf

More on carnivorous pitcher plants:

• Woodland Park Zoo - Tropical pitcher plants:
  http://www.zoo.org/page.aspx?pid=1958#.UQpReh2pBAJ

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Glossary

Carnivorous

Feeding on flesh.

Evergreen forest

Forest consisting mainly of evergreen trees, which retain leaves all year round. This is in contrast to deciduous trees, which completely lose their leaves for part of the year.

Inflorescence

The reproductive shoot of a plant, which bears a group or cluster of flowers.

Montane

Of mountains, or growing in mountains.

Raceme

An inflorescence (the flower-bearing reproductive shoot of a plant) in which the individual flowers all have distinct stalks and are attached to a central stem. The flowers at the base open first, and new flowers are produced at the tip as the shoot grows.

Tuber

In plants, a thickened stem or root that acts as an underground storage organ. Roots and shoots grow from growth buds, called ‘eyes’, on the surface of the tuber.

References

1. Mey, F., Catalano, M., Clarke, C., Robinson, A., Fleischmann, A. and McPherson, S. (2010) Nepenthes holdenii (Nepenthaceae), a new species of pyrophytic pitcher plant from the Cardamom Mountains of Cambodia. In: McPherson, S. Carnivorous Plants in their Habitats. Volume 2. Redfern Natural History Productions Limited, Poole. Available at:
   http://www.carnivorousplants.it/desc.holdenii.pdf
2. CITES (January, 2013) 
   http://www.cites.org/
3. Woodland Park Zoo - Tropical pitcher plants (January, 2013)
   http://www.zoo.org/page.aspx?pid=1958#.UQk8dR2pBAI
4. Holden, J. (2012) What’s in a name - the perils of naming new species. Flora and Fauna International Blog, 03 February. Available at:
   http://www.fauna-flora.org/whats-in-a-name-the-perils-of-naming-new-species/
5. Foges, R. (2010) New species of carnivorous plant discovered in Cambodia. Fauna and Flora International Media Release, 15 November. Available at:
   http://www.fauna-flora.org/wp-content/uploads/Media_release-New_species_of_carnivorous_plant_discovered_in_Cambodia.pdf
6. Mey, F. (2011) New Nepenthes holdenii population located! A Garden’s Chronical Blog, 08 October. Available at:
   http://carnivorousockhom.blogspot.co.uk/2011/10/new-nepenthes-holdenii-population.html