Caudiciforms (2018)

By Bob Williams (January 2018)

After experiencing Don Lesmeister’s spirited bidding at the holiday party for a Euphorbia knuthii and hearing the comments on the plant, I decided that for 2018, my articles will be based on the theme of caudiciforms or caudex-forming plants. To start the year off, I’m not going to talk about a certain plant or genus or family, but give an overview of caudex plants.

Caudiciform plants form a caudex – a fat, swollen stem, trunk or roots. Plants in this category sport colorful names like elephant’s foot, Buddha belly, pregnant onion, ponytail palm and turtle back. Their swollen caudices serve a common purpose: to store water and nutrients.

These plants grow in areas where rainfall is sparse, and temperatures can be high. They are adapted to arid climates or soil conditions, and have developed this form of storing water, rather than in foliage or in fat, leafless stems.

Caudiciforms produce green leaves and shoots during periods that are favorable for growth, and live off water and food stored in the caudex during long dry spells. To reduce evaporation, some of the plants lose their branches and vines when they dry out, leaving only the caudex and the bigger roots.

In nature, the fat-stemmed plants can attain enormous size. Baobab trees (Adansonia species) of Africa and Madagascar have swollen trunks more than 50 feet in diameter with what often looks like a modest topknot of growth to support the enormous base. The ponytail palm, Nolinia recurvata, of Mexico can have a swollen base 4 to 5 feet across.

Caudiciform plants can be divided into four general forms. Phanerophytes are those plants that have an above-ground caudex and a growing center raised above the soil level. Adeniums, most adenias, burseras, beaucarneas, cyphostemmas and pachypodiums are the most common examples.

Chamaephytes are plants with above-ground caudices with growing centers significantly closer to the ground. Dioscoreas and Euphorbia susannae are prime examples.

Hemicryptophytes are caudiciform plants with a below-ground caudex and an above-ground growing center. These plants are cultivated to show off the caudex by raising it up. Don Lesmeister’s Euphorbia knuthii, fockeas and monadeniums are some examples.

Finally, geophytes are plants that have both the caudex and the growing center underground. Plants in Ibervillea and Trochomeria, and most of the caudiciforms in the cucumber family are examples of geophytes. In all, there are over 100 genera of plants that have species that can at least loosely be described as caudiciforms.

With so many different types of plants classified as caudiciforms, there is no single care sheet. Fortunately, caudiciform plants adapt well to pot culture and are easy to grow. While generalizing is risky, their requirements are similar.

Caudiciform plants are frost-tender, and a temperature of 28 degrees F will kill most of them. Most of these plants grow during the hot summer months and are dormant during the winter, so they adapt well to moving indoors during the winter. Many species lose their leaves during winter, so a dark corner may work just as well as a sunny window. Evergreen species need a bright location during winter. A cool greenhouse maintained at 45 to 50 degrees F is perfect for overwintering most caudiciforms.

To keep the size of the plants somewhat in check and lessen the possibility of overwatering, keep the pot size of caudiciform plants relatively small for the size of the plant. When repotting, use a clay pot and a good well-drained potting soil. Some caudiciforms prefer soils of nearly pure rock, sand or pumice, or else the plants rot.

Top dressing should be with heavier rocks to add weight to the pot, because caudiciform plants are prone to becoming top-heavy. Fertilize with a houseplant fertilizer only when in growth, but feed on the modest side.

In general, water when the plants are growing and have leaves forming – which is not always when it’s warm out. It’s best to stop or at least substantially decrease watering during times of seasonal leaf loss. However, some caudiciforms are evergreens, and some don’t ever appear to be obviously growing. It is best to err on the side of less water than more if you are unsure.

There is significant information about fat plants available on the Web and from a large number of plant suppliers. One good source is http://www.bihrmann.com. This site provides a comprehensive listing of caudex plants with pictures of the plants growing in habitat.

Dave’s Garden has an excellent article on these plants. The Pacific Horticulture Society has another good article on caudiciforms at http://www.pacifichorticulture.org/articles/caudiciform-plants. A supplier, Succulent Gardening, has a good article and a wide supply of plants at http://succulents.us.

Pending Experiment
This spring, I am going to start an experiment of sorts. In my research, most sources say to plant caudiciforms in smaller pots, but a few say to overpot them. I don’t know which is correct, so I am going to find out.

I am going to buy three each of three or four different types of caudiciforms. I will plant one of each type in a 4-inch pot, another in a 6-inch and another in an 8-inch pot. I will grow them for three years without repotting to see which pot size results in the most interesting caudex.

I will take pictures during this time. If I don’t kill the plants, I will make a presentation on my findings in the fall of 2020.