Opuntia galapageia Hensl.

Galápagos prickly pear, tree prickly pear

Galápagos prickly pear cactus is found in the Galápagos Islands, at elevations up to 4921′ (1.5 km). Charles Darwin noticed that cactus finches preferred its fruits and flowers, dispersing its seeds. Doves and mockingbirds also eat the fruit. Tortoises and land animals eat the pads. A wide variety of subspecies, many unique to a single island, are both a great example of how species adapt to even slightly different conditons, and a taxonomic nightmare. Predation by various tortoise species (or lack thereof, on tortoise-free islands) likely contributed to the evolution of different forms on different islands.

Many variants previously listed as separate species or subspecies have more recently been lumped together as subspecies of Opuntia galapageia .

Plants: A shrubby or tree-like cactus. It may remain low and creeping, or become tree-like, with a woody trunk and reddish brown “bark,” reaching 8–16′ (2.5–5 m) in height. The bark is not woody, but rather composed of many layers of a honeycomb-like material, almost like corrugated cardboard. Its habit, joints, spines, and fruits are all highly variable. It may form large, sprawling thickets. Stems are a series of fleshy pads up to 1′ ⨉ 9″ (37 ⨉ 22 cm), covered with evenly spaced clusters of 1 to 28 yellowish-white or brown spines. These spines are soft and flexible instead of rigid.

Leaves: Small leaves, often dropped in the heat, are 1/16–⅛″ (2–6 mm) long.

Flowers: Yellow flowers are up to 3″ (8 cm) long.

Fruits: Fruits are large, green, and fleshy. They are approxi­mately ovoid, but highly variable in shape in size among subspecies, and usually contain multiple seeds.

Habitats: Endemic to the Galápagos Islands, at elevations up to 4921′ (1.5 km).

Here is a list of subspecies, their respect­ive islands, and older synonyms.

• Opuntia galapageia var. galapageia
  Pinta, Santiago, Floreana, San Cristóbal, Españ­ola
  Synonyms
  Opuntia galapageia var. brossettii Backeb.
  Opuntia galapageia subsp. megasperma (J.T.Howell) Guiggi
  Opuntia galapageia subvar. orientalis (J.T.Howell) Backeb.
  Opuntia megasperma J.T.Howell
  Opuntia megasperma subsp. meso­phytica (Lundh) Lodé
  Opuntia megasperma var. mesophytica
  Opuntia megasperma subsp. orientalis J.T.Howell
  Opuntia megasperma var. orientalis (J.T.Howell) D.M.Porter
  Opuntia megasperma subsp. typica J.T.Howell
  
• Opuntia galapageia subvar. barring­ton­ensis (E.Y.Dawson) Backeb.
  Santa Fe

  These are among the biggest, with trunks up to 4′ (1.2 m) around, and fruits up to 2½″ (7 cm) long when mature.

  Synonyms
  Opuntia echios var. barringtonensis
• Opuntia galapageia var. gigantea (J.T.Howell) Backeb.
  Santa Cruz

  The largest of the subspecies, they are 9½–39′ (3–12 m) tall.

  Synonyms
  Opuntia echios var. gigantea (J.T.Howell) D.M.Porter
  Opuntia echios subsp. gigantea J.T.Howell
• Opuntia galapageia var. helleri (K.Schum. ex B.L.Rob.) Backeb.
  Darwin, Genovesa, Marchena, Wolf
  Synonyms
  Opuntia helleri K.Schum.
• Opuntia galapageia subvar. inermis (E.Y.Dawson) Backeb.
  Isabela

  Found at Volcán Sierra Negra. It can reach 20′ (6 m), and produces fruits 1½–2″ (4–5.2 cm) long.

  Synonyms
  Opuntia echios var. inermis E.Y.Dawson
• Opuntia galapageia var. insularis (A.Stewart) Backeb.
  Fernandina, Isabela
  Synonyms
  Opuntia insularis A.Stewart
• Opuntia galapageia var. macrocarpa E.Y.Dawson
  Pinzon
• Opuntia galapageia var. myriacantha (F.A.C.Weber) Backeb.
  Baltra, Daphne, and some of the smaller islands

  Occurs in both treelike and shrubby forms, and may reach 9½′ (3 m) tall. Seeds are 1/16–⅛″ (2–3 mm) long.

  Synonyms
  Opuntia echios
  Opuntia galapageia var. echios
  Opuntia myriacantha F.A.C.Weber
• Opuntia galapageia var. profusa E.F.Anderson & Walk.
  Isabela, Santiago, Rábida

  These never exceed the size of a large shrub, 3–6½′ (1–2 m) tall. Resembles a heap of jumbled pads.

• Opuntia galapageia var. saxicola (J.T.Howell) Backeb.
  Isabela
  Synonyms
  Opuntia saxicola J.T.Howell
• Opuntia galapageia var. zacana (J.T.Howell) Backeb.
  North Seymour

  These never exceed the size of a large shrub, 3–6½′ (1–2 m) tall.

  Synonyms
  Opuntia zacana J.T.Howell
  Opuntia echios var. zacana (J.T.Howell) Backeb.

Online References:

References:

 

Opuntia galapageia description by Thomas H. Kent, not updated.

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