buttonbush

(Cephalanthus occidentalis)

Conservation Status
buttonbush
Photo by Greg Watson
  IUCN Red List

LC - Least Concern

     
  NatureServe

N5 - Secure

S4 - Apparently Secure

     
  Minnesota

not listed

     
           
  Great Plains

OBL - Obligate wetland

     
  Midwest

OBL - Obligate wetland

     
  Northcentral & Northeast

OBL - Obligate wetland

     
         
 
Description
 
 

Buttonbush is a tall, deciduous shrub rising on multiple stems from a woody, branching, root system. Individual stems can be 3 to 10 tall and 1 to 4 in diameter at breast height, but in the northern parts of its range, which includes Minnesota, they are rarely more than 6 tall and 3 in diameter at breast height. The plant rarely takes the form of a small tree up to 16½ (5 m) tall.

Buttonbush occurs in the United States and southern Canada east of the Great Plains, in Mexico, and in Central America. There are also disjunct populations in Arizona and in California. It is uncommon in Minnesota, where it is mostly restricted to the floodplains of the Mississippi and St. Croix Rivers, and a disjunct population in Rice County. It is found in floodplain forests and shrubby swamps; at the edges of marshes and bogs; on river banks and lake shores; and in disturbed areas. It grows under full or partial sun in wet to moist areas on fertile soil with high organic content. It sometimes forms dense thickets in floodplains by sprouting roots from the base of the stem which then become detached, creating a new plant (layering).

The stems are usually erect but sometimes recline on the ground with just their tips ascending (decumbent). They are round to somewhat four-sided, and are frequently branched. The bark is dark brown, thick, and furrowed, with flat-topped ridges.

The branches are slender and spreading, giving the plant a bushy appearance. First year twigs are slender, hairless, and green. Second year twigs are moderately stout, hairless, reddish-brown or grayish-brown, and speckled with whitish, elongated openings (lenticels). The terminal bud is usually absent because the tip of the twig usually dies back. Lateral buds are small and are embedded within the bark. Leaf scars are D-shaped or nearly round and have a single U-shaped bundle scar.

Leaves are 1 to 6 (2.5 to 16 cm) long, ¾ to 2 (2 to 6 cm) wide. They are mostly opposite but some leaves may be in whorls of three. They are on slender, hairless, to 1 (10 to 25 mm) long leaf stalks (petioles). Between the bases of each pair of opposite leaves there is a single small appendage (stipule) on each side of the stem. (Most plants in the Rubiaceae family have these interpetiolar stipules, and this is an important identifying feature of the family. In other families, most plants with opposite leaves and stipules have a pair of stipules at the base of each leaf, with four stipules at each node.) The stipules are 116to (2 to 4 mm) long, triangular, and sharply pointed. They generally persist as long at the leaf. The leaf blades are unlobed, oval and broadest at the base (egg-shaped) or in the middle (elliptic), rounded or angled at the base, and angled or tapered to a sharply pointed tip. The upper surface is dark green, hairless, and sometimes shiny. The lower surface lighter green and usually hairless, sometimes with hairs on the main veins. There is a prominent midrib and 6 to 8 pairs of lateral veins. They are strongly depressed on the upper surface, strongly raised and conspicuous on the lower surface. The margins are flat and untoothed. They often have a fringe of minute hairs. The leaves appear relatively late in the season.

The inflorescence is a dense, globe-shaped, to 1916 (1 to 4 cm) in diameter, head-like cluster of 100 to 200 flowers. The flowers appear in late June to early August in a loose branched cluster at the end of the stem and sometimes singly from the upper leaf axils. Each cluster is on a stout, ¾ to 2 (1.5 to 6 cm) long stalk (peduncle) or peduncle branch. The flowers are intermingled with short, green, narrowly club-shaped inflorescence leaves (bracts).

Each flower has 4 sepals, 4 petals, 4 stamens, and 1 style. The sepals are united into a short, green, tube-shaped, four-lobed calyx. The lobes are rounded and just 164 (0.4 to 0.5 mm) long when flowering, doubling in length and persisting when fruiting. The petals are white and to ½ (9 to 12 mm) long. There are fused into a tube-shaped corolla with four slightly spreading lobes at the tip. The outer surface is hairless and the inner surface is hairy, especially at the upper part of the tube. The lobes are narrowly elliptic, 116to (1.5 to 2.5 mm) long, and bluntly pointed at the tip. The stalks (filaments) of the stamens are as long as the corolla tube. The anthers extend beyond the throat of the tube. The style has a long stalk and extends well beyond the tube.

The fruit is a dry, brown, cone-shaped, 316 (5.0 to 5.5 mm) long, 132 to 116 (1.5 to 2.0 mm) wide capsule. The capsules develop in a single globe-shaped mass but separate at maturity. Each capsule has two cells, each cell a single seed.

 
     
 

Height

 
 

3 to 16½

 
     
 

Flower Color

 
 

White

 
     
 

Similar Species

 
     
     
 
Habitat
 
 

Wet to moist. Full or partial sun. Floodplain forests, shrubby swamps, edges of marshes and bogs, river banks, lake shores, and disturbed areas. Full or partial sun, Fertile soil with high organic content.

 
     
 
Biology
 
 

Flowering

 
 

Late June to early August

 
     
 
Use
 
 

 

 
     
 
Distribution
 
 

Distribution Map

 

Sources

2, 3, 4, 5, 7, 8, 24, 28, 29, 30.

 
  8/21/2021      
         
 

Nativity

 
 

Native

 
         
 

Occurrence

 
 

Uncommon in Minnesota

 
         
 
Taxonomy
 
  Kingdom Plantae (green algae and land plants)  
  Subkingdom Viridiplantae (green plants)  
  Infrakingdom Streptophyta (land plants and green algae)  
  Superdivision Embryophyta (land plants)  
  Division Tracheophyta (vascular plants)  
  Subdivision Spermatophytina (seed plants)  
  Class Magnoliopsida (dicots)  
  Superorder Asteranae  
 

Order

Gentianales (gentians, dogbanes, madders, and allies)  
 

Family

Rubiaceae (madder)  
 

Subfamily

Cinchonoideae  
 

Tribe

Naucleeae  
 

Genus

Cephalanthus (buttonbush)  
       
 

Subordinate Taxa

 
 

Two varieties of buttonbush have been described, but these are not generally accepted. Of the two, only the hairless nominate variety Cephalanthus occidentalis occidentalis occurs in Minnesota.

 
       
 

Synonyms

 
 

Cephalanthus occidentalis var. californicus

Cephalanthus occidentalis var. pubescens

 
       
 

Common Names

 
 

buttonbush

button-willow

commom buttonbush

honye-bells

 
       

 

 

 

 

 

 

Glossary

Axil

The upper angle where a branch, stem, leaf stalk, or vein diverges.

 

Bract

Modified leaf at the base of a flower stalk, flower cluster, or inflorescence.

 

Bundle scar

Tiny raised area within a leaf scar, formed from the broken end of a vascular bundle.

 

Calyx

The group of outer floral leaves (sepals) below the petals, occasionally forming a tube. Plural: calyces.

 

Decumbent

Reclining on the ground but with the tip ascending.

 

Filament

On plants: The thread-like stalk of a stamen which supports the anther. On Lepidoptera: One of a pair of long, thin, fleshy extensions extending from the thorax, and sometimes also from the abdomen, of a caterpillar.

 

Layering

A method of propagation where a stem or branch comes into permanent contact with the soil, sprouts roots, and then detaches from the main plant.

 

Lenticel

A corky, round or stripe-like, usually raised, pore-like opening in bark that allows for gas exchange.

 

Node

The small swelling of the stem from which one or more leaves, branches, or buds originate.

 

Peduncle

In angiosperms, the stalk of a single flower or a flower cluster; in club mosses, the stalk of a strobilus or a group of strobili.

 

Petiole

The stalk of a leaf blade or compound leaf that attaches the leaf blade to the stem.

On plants: The stalk of a leaf blade or compound leaf that attaches the leaf blade to the stem. On ants and wasps: The basal stalk of the abdomen.

 

Stipule

A small, leaf-like, scale-like, glandular, or rarely spiny appendage found at the base of a leaf stalk, usually occurring in pairs and usually dropping soon.

 
 
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Greg Watson

 
  I noticed that you don’t have a page for Buttonbush, Cephalanthus occidentalis. I attached a couple of pictures of one that is growing on the Wagon Wheel Trail in La Crescent, MN.

 

  buttonbush  
           
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Other Videos
 
  Cephalanthus occidentalis (buttonbush)
NC State Dendrology
 
   
 
About

Aug 17, 2020

 
  buttonbush (Cephalanthus occidentalis)
UF/IFAS Center for Aquatic and Invasive Plants
 
   
 
About

May 19, 2010

Aquatic and Invasive Plant Identification Series by the UF/IFAS Center for Aquatic and Invasive Plants ( http://plants.ifas.ufl.edu ) and the Florida Fish and Wildlife Commission, Invasive Plant Management Section.

For more information about buttonbush, go to http://plants.ifas.ufl.edu/node/93

Video editor/videographer - Phil Chiocchio

 
  Buttonbush - Cephalanthus occidentalis
Ionxchange
 
   
 
About

Sep 10, 2011

Earthyman views Buttonbush (Cephalanthus occidentalis) in bloom on Mississippi River Wetland in Wisconsin. Seed and plants are sold at Ion Exchange, native seed and plant nursery. http://www.ionxchange.com

 
  Cephalanthus occidentalis Buttonbush
Steven Kristoph
 
   
 
About

Jul 5, 2021

A large growing native shrub being pollinated by many bumble bees.

 
       

 

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  Greg Watson
6/27/2021

Location: Wagon Wheel Trail in La Crescent, MN

I noticed that you don’t have a page for Buttonbush, Cephalanthus occidentalis. I attached a couple of pictures of one that is growing on the Wagon Wheel Trail in La Crescent, MN.

buttonbush  
           
 
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Created: 8/21/2021

Last Updated:

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