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Subfamilies of the Malvaceae on Palomar College Campus
Including Some Other Interesting Species Encountered On My Travels
© W.P. Armstrong 2023   
Introduction: The mallow family (Malvaceae) contains some of the most beautiful native & naturalized wildflowers on our planet. It also includes many ornamental trees & shrubs, and some economically important species, including cotton & okra. Now several additional economically important families have been merged with the Malvaceae, including the chocolate family (Sterculiaceae: Cacao & cola nut), the basswood family (Tiliaceae: Basswood & jute), and the bombax family (Bombacaceae: Kapok & balsa). The Palomar College campus & Arboretum has a impressive collection of plants in the Malvaceae, including different subfamilies that were formerly classified in separate plant families.

Economically Important Species in the Malvaceae: Left: Kapok (Ceiba pentandra), formerly in the bombax family (Bombacaceae). Center: Okra (Hibiscus esculentus). Right: Cotton (Gossypium) tetraploid hybrid).

Native Malvaceae (Subfamily Malvoideae) in San Diego County

Beautiful California native wildflowers in the Malvaceae: Left: Bush Mallow (Malacothamnus fasciculatus) in Palomar College Arboretum. Center: Apricot mallow (Sphaeralcea ambigua var. ambigua). Right: Desert 5-Spot (Eremalche rotundifolia). There are many more lovely native species.

Two former members of the cacao or chocolate family (Sterculiaceae) native to San Diego County. They now reside in the Malvaceae (subfamily Malvoideae). Left: Flannelbush (Fremontodendron californicum ssp. californicum), a colorful shrub native to shady desert canyons of the Laguna Mountains. Right: Ayenia compacta, an interesting little shrub native to rocky desert canyons. The unusual petal claws (stalks) are threadlike and curved.
Phylogenetic trees (cladograms) are based on shared, derived characters that are entered into a computer. In other words, the phylogenetic trees reflect shared traits derived from common ancestry. Taxonomic groups that reflect a common ancestor are termed monophyletic. For example, all birds and reptiles are thought to have descended from a single common ancestor and are monophyletic. Humans (Homo) and chimpanzees (Pan) are also monophyletic.

DNA studies clearly show that the chocolate family (Sterculiaceae), basswood family (Tiliaceae), and bombax family (Bombacaceae) are not monophyletic. They are better treated as subfamilies within the mallow family (Malvaceae). When I wrote the duckweed family (Lemnaceae) section for the Jepson Flora of California it was necessary to reduce it to subfamily Lemnoideae within the Arum family (Araceae) to comply with monophyletic requirements. Maintaining duckweeds (Lemnaceae) and arums (Araceae) as distinct families would make the arum family paraphyletic, with a common ancestor but without all of its descendants (i.e. duckweeds were excluded). Although they certainly appear very different, duckweeds are genetically related to arums. In order to have a monophyletic, computer-generated cladogram, the duckweeds are now placed in the family Araceae.

  Naturalized Mallow Species: Twin Oaks Valley  
  Bottle Tree Images: Palomar College Campus  

Plants On Palomar College Campus & Arboretum. Some Belonged To Non-
Monophyletic Families. They Now Reside in Subfamilies Within Malvaceae

1. Subfamily Malvoideae

Bush Mallow (Malacothamnus fasciculatus) 27 March 2022

This native shrub is a dominant species in the post-burn coastal sage scrub plant community east of campus. Since the Comet Fire of January 2021 and massive post burn bloom of 2022, the cottonseed bug of campus (Oxycarenus hyalinipennis) has been detected in this area.

  Palomar College Fire Images Home Page  

Hibiscus taiwanensis: A beautiful shrub native to Taiwan. There are over 200 species of Hibiscus, including some rare endemics in the Hawaiian Islands.

Flowers of beach hibiscus (Hibiscus tiliaceus), a common shrub along tropical Pacific beaches. The beautiful yellow blossoms turn pinkish-red with age. The bark contains strong bast fibers. Strips of bark are woven into cordage and mats, and make excellent "grass" skirts. Photo from Palomar biology field trip to French Polynesia.

The cow itch tree or Norfolk Island hibiscus (Lagunaria pattersonii) produces seed capsules lined with numerous stiff hairs. The trichomes can irritate the skin if the pods are handled carelessly. This species is native to Lord Howe Island, Norfolk Island, parts of coastal Queensland, Australia and parts of northeastern New South Wales.

Longitudinal section through seed capsule of cow itch tree (Lagunaria pattersonii) showing masses of silvery-silky hairs (trichomes) that line inner walls. Under high magnification (100x) they appear to be unicellular epidermal outgrowths. As I said in previous caption, the trichomes can irritate the skin if the pods are handled carelessly, and are sometimes referred to as urticating hairs. Good examples of stinging trichomes are nettles (Urticaceae), Mucuna pods (Fabaceae), and Wigandia (Now in family Boraginaceae). In fact, latter plant grows in Palm Section of Palomar College Arboretum.

  Plants With Stinging Trichomes  

Callianthe tridens (syn. Arbutilon tridens): A Central American shrub (Mexico to Guatemala) showing fruit (cluster of schizocarps) and branched (stellate) epidermal hairs (trichomes) on underside of leaves. Stellate trichomes occur in many plant families. In southern California oaks (Quercus), the shape of stellate hairs can be helpful in species identification.

  Hibiscadelphous distans: A Very Rare Endemic On The Island Of Kauai  

Hibiscadelphus distans is an extremely rare species of flowering plant in the mallow family (Malvaceae) that is endemic to the Hawaiian island of Kauai. It is a bush or small tree with heart-shaped leaves that grows between 1,000 and 1,800 feet (300 and 550 m) in the remnants of native dry forests. Despite its rarity, it is believed to be the only surviving species in the genus Hibiscadelphus which is only known from the Hawaiian Islands. The other five species have recently become extinct in the wild, some being known from only a single plant.

The flowers have the typical structure of mallows with style surrounded by a sheath of monadelphous stamens united by their filaments and exerted filiform stigmas; however, in my opinion they superficially appear quite distinct from other mallow blossoms in this fascinating plant family. The foliage is also covered with star-shaped hairs (stellate pubescence), also typical of many members of the Malvaceae. This rare specimen is where I saw my first cottonseed bug (Oxycarenus hyalinipennis) on the Palomar College campus. Special thanks to iNaturalist for confirming ID of this very serious destructive insect of the mallow family.

More Subfamiliy Malvoideae Species At Palomar College

A. Malva subovata (syn. Lavatera maritima) Mediterranean Bush Mallow; B. Phymosia umbellata Mexican Bush Mallow; C. Sida fallox Golden Mallow (Hawaiian Islands); D. Talipariti elatum Blue Maloe (Jamaica & Cuba).

A. Hibiscus mutabilis Cotton Rose (China); B. Hibiscus schizopetalus Spider Hibiscus (Central Africa); C. Malvaviscus arboreus Turk's Cap (s. U.S. to South America); D. Arbutilon grandifolium Indian Mallow (South America & Africa; naturalized throughout world).

2. Subfamily Bombacoideae

Ceiba speciosa (Floss Silk Tree)
Formerly Placed in the Bombax Family Bombacaceae.
Native to South America.

Floss Silk Tree (Ceiba speciosa), formerly Chorisia speciosa: A deciduous tree native to tropical and subtropical forests of South America. It belongs to the same genus as kapok tree (Ceiba pentandra), native to Central and South America. Both species produce seed capsules lined with masses of silky hairs.

Red silk cotton tree (Bombax ceiba)), formerly in the bombax family (Bombacaceae). Like kapok and floss silk trees, the seed capsules are lined with masses of silky hairs. A large deciduous tree native to India-S. China & Tropical S.E. Asia, this species has truly spectacular flowers.

3. Subfamily Tilioideae

Tilia americana (American Linden or Basswood)
Formerly Placed in the Family Tiliaceae.
Native to Eastern United States.


Tilia americana

The distinctive leaf-like bracts and fruits of the American linden (Tilia americana). Also known as basswood, prepared microscope slides of stem cross sections from this species are commonly used in general botany and plant anatomy classes.

4. Subfamily Dombeyoideae

Dombeya cayeuxii (Pink Snowball Tree)
Formerly Placed in the Family Sterculiaceae.
Native to Africa & Madagascar.


Dombeya cayeuxii

 		Dombeya autumnalis in the Palomar Arboretum, correctly named the Edwin & Frances Hunter Arboretum at Palomar College. This interesting species is called "Autumn Dombeya." It is native to South Africa.

5. Subfamily Sterculioideae

Firmiana simplex (Chinese Parasol Tree)
Formerly Placed in the Chocolate Family Sterculiaceae.
Native to Eastern Asia (China).


Firmiana simplex

Putrid Flowers Of Indian Almond Formerly In The Sterculiaceae
Stinking flowers are by no means limited to herbaceous perennials. In fact, a large rain forest tree of the Old World tropics called Indian almond (Sterculia foetida) produces masses of small, reddish-orange flowers with a disagreeable putrid stench. It belongs to the chocolate family (Sterculiaceae = Malvaceae) and produces edible seeds inside large, woody pods called follicles. The oily seeds are eaten raw, roasted or fried; however, if consumed in excessive quantities the seeds may have a purgative effect. The smelly blossoms leave a long-lasting, putrid scent in your carrying case or pack. This certainly happened to my backpack on a trip to the Hawaiian Islands.


Flowers and a follicle seed pod of "stinky sterculia" or Indian almond (Sterculia foetida). A. View of seeds inside one follicle (carpel). B. Flowers from the inflorescence. C. Close-up view of one flower. D. Mature fruit composed of 5 many-seeded follicles. The speciific epithet foetida is derived from the putrid odor of the blossoms. This species is also called "Java almond" and the seeds are eaten raw, roasted or fried. It was formerly placed in the family Sterculiaceae; however DNA cladistical analysis shows that it belongs in the mallow family (Malvaceae). I once placed the flowers and seed pods of this tree into a luggage bag and the putred odor in my bag persisted for several years!

Drift Fruits In The Mallow Family (Malvaceae),
Some Of These Formerly In The Sterculiaceae:
  Interesting Drift Fruits & Seeds That Ride The Ocean Currents  
During the late 1980s & 1990s, I went on many Palomar College marine biology field trips to the Yucatan Peninsula, Caribbean, Central & South America with my dear colleagues Lester Knapp, Nancy Jessop, Robert Ebert and Candice Francis. Since I was not an avid snorkler or scuba diver, I specialized in the identification of drift fruits and seeds that wash ashore on tropical beaches, some of which can travel for months at sea and thousands of miles to distant continents. I recently discovered that two of the species in above link are members of the mallow family (Malvaceae).

One of the most remarkable drift fruits (F on above link) is the dry seed pod of Heritiera littoralis (formerly in the Sterculiaceae), an Asian tree of mud flats and river deltas. The common name "looking glass mangrove" refers to the silvery underside of leaves that resembe mirrors. It is also called "keel-pod mangrove" for obvious reasons. The woody fruit contains space around the seed for buoyancy and is keeled, presumably to aid in flotation. It is native to Asia, Southeast Asia and Tropical Africa, with a drift range from Madagascar to the Fiji Islands. It has also been reported from the northern coast of Europe and as far north as Finland. However, according to article in The Drifting Seed by Mikko Piirainen of the Finnish Museum of Natural History, these curious pods have been imported to the Netherlands and are sold in flower shops. They may have been dispersed by people. By the way, I did not find my Heritiera pod in the Caribbean. I am not sure where I got it (possibly a shop selling sea shells), but it certainly is one of my favorite drift fruits.

The Australian bottle tree (Brachychiton rupestris), shown here in the Palomar College Arboretum, is another species formerly placed in the chocolate family (Sterculiaceae). There are several photogenic specimens with large, swollen trunks on the main campus, along with other species in the fascinating Australian genus Brachychiton. These species are monoecious with separate male (pollen-bearing) and female (seed-bearing) flowers on the same tree. I placed most of the images on another page to reduce the number of images and loading time for this page. See link to other species below.

Brachychiton rupestris (bottle tree) in Palomar College Arboretum. Campus trees do not bloom that often, so I used flower image from Wikimedia Commons: Melburnian, CC BY-SA 3.0 (creativecommons.org/licenses/by-sa/3.0). The seed-bearing fruits (technically called follicles) are much smaller than other species of Brachychiton on Palomar College campus.

Monoecious Flame Tree (Brachychiton acerifolius) On Campus

  Bottle Trees (Brachychiton) at Palomar College  

6. Subfamily Grewioideae

Grewia occidentalis (Lavender Star Flower)
Formerly Placed in the Family Tiliaceae or Sparmanniaceae.
Native to South-Eastern Africa.


Grewia occidentalis

Monkeycomb Formerly In The Basswood Family (Tiliaceae)

Fruits of the monkeycomb (Apeiba aspera), an interesting Costa Rican tree in the subfamily Grewioideae. A. Large fruit covered with spines that superficially resembles a sea urchin. The fruits are used as hair brushes and are sold in the marketplace. B. Fruit with the spines worn off that resembles the tuberculate test (shell) of a sea urchin. C. The tuberculate test (shell) of a sea urchin.