Family Rosaceae Units 23 - 26 part

1. Rosaceae Family

Trees, shrubs, and herbs.

Leaves alternate (rarely opposite), simple or compound or dissected.

Stipules usually present, but lacking in Spiraea.

Generally grow best in a well drained soil, with full sun, and pH of 6.0 to 6.5.

2. Hypanthium

Most Rosaceae members have a hypanthium. This is a floral cup or tube to which the

flower parts are attached. It is formed by the united base of sepals, petals, and

stamens.

3. Apomixis and Polyploidy

The taxonomy of some larger genera like Rubus (Raspberries), and Crataegus

(Hawthorns) is complicated by polyploidy and apomixis.

Apomixis is an asexual type of reproduction through seed, without fertilization.

The plant embryos grow from egg cells without being fertilized by pollen

(the male part of the plant).

Polyploidy refers to multiple sets of chromosomes.

4. Rosaceae Classification

The Rosaceae have four or more subfamilies which some authors elevate to family

status. The subfamilies are:

a. Subfamily Spiraeoideae

          Stipules absent, many ovules, fruit a follicle (dry and dehisce or split along

one margin) or capsule (dry and dehisces along several sides). Stipules are leaf like

and attached at the base of the leaf stalk. Stipules are kidney shaped in Chaenomeles

and persist, making them a key identification characteristic.

          Spiraea = Spiraea

b. Subfamily Rosoideae

          Single ovule, fruit an achene or drupelets.

          Rubus = Raspberry and blackberry

          Fragaria = Strawberry (achenes in an enlarged fleshy receptacle; the strawberry

that we eat)

c. Subfamily Prunoideae

          Single ovule, fruit a drupe (fleshy outside with a stony covering around the

seed).

          Prunus = Stone fruits such as almond, apricot, cherry, plum,

peach

d. Subfamily Maloideae or Pomoideae

          Fruit a pome that has 2 to 5 carpels with several seeds. A pome is a fleshy fruit

with the seeds encased within a cartilaginous wall.

          Cydonia = Quince

          Eriobotrya = Loquat (Florida and tropics)

          Malus = Apple, crabapple

          Pyrus = Pear

5. Common Disease problems in the Rosaceae

a. Scab is a fungus disease on crabapples and apples (Malus).

b. Fire Blight is a bacterial disease that is often fatal. Bees even carry it while collecting

honey. Found especially on Amelanchier, apples and crabapples (Malus), Cotoneaster,

hawthorns (Crataegus), mountain ash (Sorbus), and firethorn (Pyracantha).

c. Rust Diseases.

Cedar apple rust is a fungal disease on apples and crabapples (Malus). It has an

alternate host, meaning that part of the rust life cycle is on Juniperus or cedar.

Cedar hawthorn rust is on hawthorn (Crataegus), with part of its life cycle on Juniperus.

6. Common Insect problems in the Rosaceae

a. Gypsy Moth was introduced from Europe. The larvae feed on and defoliate most

hardwood trees, but they seem attracted to purple leaved cultivars of Acer

platanoides (Norway Maple), and some Malus (Crabapples).

They prefer Prunus (Cherries), but also attack apples and crabapples (Malus),

Crataegus (Hawthorns), Cotoneaster, etc.

b. Eastern Tent Caterpillar has larvae that form tents in the crotches of trees.

They will defoliate the branches where they feed. They are commonly maintained

on the native Choke Cherry Prunus virginiana, which is spread by birds eating

the fruit.

There are also Fall Webworm and other insects that form tents on branches.

7. Common Animal problems in the Rosaceae

Animals can be a problem, since Rosaceae plants seem to have a tasty bark.

a. Mice are rodents (Order Rodentia) that can girdle trees at the base of the trunk.

Keep mulch and ground covers away from the base of small trees, since they

provide cover for the mice.

b. Rabbits often girdle plants higher up on the stems. They commonly do damage

when there is snow cover in the winter. Stems of small shrubs are commonly

chewed, and the cambial or growth layer is destroyed, so the branches die in the

spring. Besides tasty Rosaceae plants, Euonymus alata (Burning Bush) is also

commonly attacked.

Rabbits are in the Order Lagomorpha and are not rodents.

Wire mesh (hardware cloth) can be wrapped around the trunks, but it must be high

enough to thwart a rabbit standing on the crusted snow.