GREENHOUSE TOUR No. 2
Floristics, Disjuncts, Evolution
Plant Geography
Botany 422- 2024
Greenhouse 1 (Research House)
1. Amborella trichopoda — amborella (Amborellaceae)-
A special shrub endemic to New Caledonia – it is the only species in this ancient family, the species, genus, and
family are all endemic to this island known as a world biodiversity hotspot. Amborella is also special in that
DNA evidence indicates that it is “sister” to all other 400,000 or so flowering plants. Typical of many island
plants, the shrub is dioecious – there are male plants with only stamens and there are female plants with only
carpels in their flowers.
2. Gossypium — Mexican upland cotton (Malvaceae)
This is the common cotton (Gossypium hirsutum) that is cultivated in southern North America and now around
the world – it accounts for 90% of commercial cotton production worldwide. The species is an allopolyploid
and is derived from an African species (which dispersed to the Americas about 1-2 million years ago)
hybridizing with a New World species followed by doubling of the chromosomes. Transoceanic long-distance
dispersal is not restricted to this species, as Gossypium tomentosum (a Hawaiian endemic) growing next to the
cultivated cotton evolved following dispersal from the Americas. Its closest relative is the Mexican upland
cotton.
3. Salvia — sage (Lamiaceae)
One of the largest genera of flowering plants, with nearly 1,000 species, which now includes the culinary
rosemary (Rosmarinus) elsewhere in the greenhouses. The aromatic sages arose in SW Asia about 32 mya, but a
single dispersal event to North America across Beringia gave rise to a great radiation of Mexican to South
American sages of about 500 species to which these two species belongs. Many of these New World sages
retained the ancestral bee pollination syndrome (note the blue, two-lipped flowers on Salvia cendrosensis,
endemic to Baja California). Part of this “adaptive radiation” involved a key switch to hummingbird
pollination (note the red tubular flowers on Salvia rubescens, endemic to Venezuela) about 20 mya, just after
ancestral hummingbirds invaded the New World from Europe.
Greenhouse 2 (Tropical House)
4. Malpighia glabra — Barbados cherry (Malpighiaceae)
This species, also known as acerola or wild crape-myrtle, is a tropical shrub or small tree. It ranges from
southern Texas south through Mexico and the Caribbean to Peru and Brazil. It is widely cultivated for its fruits
which are high in vitamin C. Although the family is primarily pantropical, historical biogeographical analysis
indicates that primitive members first evolved in temperate regions of the Northern Hemisphere and
subsequently radiated separately into the different tropical regions of the world – consistent with the
“Boreotropics Hypothesis”.
5. Coffea arabica — coffee (Rubiaceae)
The pits in the fruits are the coffee beans of commerce. Native to tropical Africa, this species is cultivated in
tropical areas worldwide — providing a nice example of the common pattern seen in the biogeography of
cultivated plants, where a species is often a more economically important crop outside its native range.
Coffee is often grown as a shade crop, a system that mimics the commonest ecological role of members of this
family — understory shrubs in tropical rainforests. A recent genomic study has demonstrated that “caffeine”
biosynthesis has evolved in parallel in the unrelated stimulants coffee, tea, and cola.
Greenhouse 3 (Orchid House)
6. Welwitschia mirabilis (W. bainesii) — (Welwitschiaceae)
This ancient gymnosperm endemic is found only in the Namib Desert of southwestern Africa and the only
species of its family. Note the peculiar morphology – a caudex producing two leaves with basal meristems.
These leaves later fray so as to appear more numerous. It has a taproot to 3 m deep but this just serves to
anchor the plant and doesn’t absorb or transport water. Since it virtually never rains where this plant grows, it
has adapted as a nephelophyte by getting its water via fog absorbed by stomata on the upper leaf surface.
[See the display case on the Birge 1st floor hallway near room 122.]
7. Canariana canariensis — Canary Island bellflower (Campanulaceae)
A genus endemic to the Canary Islands, this species has waxy evergreen, toothed leaves adaptive in the laurel
forests. It has a tuberous stem from which emerge scrambling hollow stems and large, bell-shaped pendent
flowers. These flowers produce copious amounts of hexose-rich nectar and are bird-pollinated by native,
passerine (perching) Canary Islands chiffchaffs – other similar appearing bellflowers in the Andes of South
America are pollinated by hummingbirds and bats.
Greenhouse 4 (Tropical House)
8. Rhipsalis — mistletoe cactus (Cactaceae)
Rhipsalis is the only genus of cacti that occurs naturally in the Old World, represented by one epiphytic species
that ranges across Africa to Madagascar and Sri Lanka: another case of long distance dispersal in this case by
birds that ingest the fleshy white fruits seen on this plant. There are many species of epiphytic cacti (such as
the Christmas cactus) in the New World; they are found in both dry and wet habitats. Succulence and CAM
(Crassulacean Acid Metabolism) are “pre-adaptations” to epiphytism.
9. Nepenthes — Asian pitcher plant (Nepenthaceae)
Nepenthes, only genus in the family, are carnivorous plants that are easy to recognize because of the lidded
pitchers borne on the end of a twining prolongation of the leaf tip. This genus is found throughout Indonesia,
extending to Australia, with a few species disjunct in Madagascar, Sri Lanka, and the Seychelles — a common
north Indian Ocean arc distribution pattern. One species produces nectar from the lid of its trap which attracts
tree shrews that sit and lick the nectar, sometimes defecating into the pitcher! The plant then absorbs these
nutrients; an example of plant coprophagy. Note the similarity of Asian pitcher plants to the unrelated
American pitcher plants (Sarracenia, Sarraceniaceae) seen in the back of greenhouse #6 – another striking
instance of convergent evolution in solving the same ecological problem (lack of nitrogen) by forming pitcher
plants for carnivory in unrelated groups in different areas of the world.
Greenhouse 5 (Begonia House)
10. Stegolepis — stegolepis (Rapateaceae)
This small family contains ~100 species in 16 genera and is almost completely restricted to South America with
one monotypic genus (Mascocephalus) in West Africa. The majority of the species grow in the Guyana
Highlands atop giant sandstone tepuis. These “sky islands” have allowed the group to radiate in isolation and
many tepuis have their own endemic species. Either bees or hummingbirds pollinate species in this family.
DNA evidence has shown that the enigmatic African species arose ~ 6 million years ago, well after South
America split from Africa. This confirmed the hypothesis that long distance dispersal is the cause of this
strange distribution.
Greenhouse 6 (Cool House)
11. Pelargonium — geranium (Geraniaceae)
Pelargonium is native to southern Africa (including Namibia) and Australia. Southern Africa contains 90% of
the genus, with only about 30 species found elsewhere, predominantly the East African rift valley (about 20
species) and southern Australia, including Tasmania. This group is representative of the great species
diversity endemic to South Africa and why the Cape region is considered the 6th Floristic Kingdom or Realm.
The strong scent of the leaves, anti-herbivory, is common in Mediterranean biome regions (e.g., mint family).
North American “geraniums”, such as common in the temperate forests of Wisconsin, belong to another
genus, Geranium.
12. Fuchsia — fuchsia (Onagraceae)
This woody genus is largely tropical/temperate South American with an extensive radiation in the Andes
where they have co-evolved with hummingbirds. However, one group of species occurs in New Zealand and
Tahiti. The fossil record indicates that the genus is an example of an element of the great southern hemisphere
temperate flora that broke apart roughly 30-50 mya. Much more recent long distance dispersal has given rise
to the species in Tahiti. Interestingly, Fuchsia is now known to be most closely related to the high latitude,
Northern Hemisphere herbaceous genus Circaea (enchanter’s nightshade), which is found in Wisconsin.
13. Eucalyptus — eucalyptus (Myrtaceae)
This is a characteristic genus of aromatic-leaved trees and shrubs in Australia, containing about 500 species,
with only two or three extending north into Malaysia, west of Wallace’s Line. The species have diversified in
moisture gradients ranging from temperate rainforests to Mediterranean to desert conditions. Many species
are cultivated in tropical, subtropical, and Mediterranean regions throughout the world as fast growing
sources of timber and firewood. Some species have become aggressive weeds in Africa, California, and
Hawaii where introduced.
Greenhouse 7 (Succulent House)
14. Alluaudia — Madagascar ocotillo (Didiereaceae)
The genus and entire family of 11 species are endemic to Madagascar and belong to the same order as the
American family Cactaceae. This plant is a spiny succulent shrub, with thick water-storing stems and leaves
that are deciduous in the long dry season. Although strikingly similar in appearance, it is not at all related to
the American ocotillo, Fouquieria splendens of the Sonoran Deserts in North America which can be seen next to
it – a striking example of evolutionary convergence in unrelated species via natural selection in similar
biomes.
Greenhouse 8 (High House)
15. Caryota — fishtail palm (Arecaceae)
These palms are known as fishtail palms because of the lacerated shape of their leaflets. The genus is almost
strictly Asian and is a botanical example of a group that largely honors the Wallace Line by occurring west of
it. One more recently derived species occurs east of the Wallace Line – perhaps evolving after the Australian
and Asian plates collided. Other fishtail palms are growing in the Birge Hall lobby.