ROSIDAE

The subclass Rosidae contains the largest number of families of any subclass of flowering plants. The subclass consists of over 58,000 species, 114 families, and 18 orders. It has about the same number of species as the subclass Asteridae. Five orders, Fabales (14,000 species) Myrtales (9000 species), Euphorbiales (7600 species), Rosales (6600 species) and Sapindales (5400 species), contain about 75% of the species in the subclass.

Rosales

A diverse and almost certainly paraphyletic group, the Rosales is difficult to characterize. The flowers tend to be actinimorphic, the perianth 5-merous and differentiated into calyx and corolla. Many members of the order are monocarpous or apocarpous, and there is a trend towards elaboration of a hypanthium, resulting in perigyny and epigyny. However, none of these characteristics is diagnostic of the order as a whole.

 

Both the Rosaceae and Saxifragaceae are extremely diverse families, and they can at times be difficult to distinguish. In general, the Saxifragaceae lack stipules, have 10 or fewer stamens, albuminous seeds, and usually have a syncarpous gynoecium whereas the Rosaceae mostly have stipule, have numerous stamens (well over 10) , have exalbumious seeds, and have an spocarpours or monocarpour gynoecium (except subfamily Maloideae)

 

Some herbaceous members of subfamily Rosoideae in which the hypanthium is not well developed bear a striking resemblance to some Ranunculaceae (e.g. Potentilla vs. Ranunculus). The best field character to look for when this problem arises is the presence of stipules (Rosaceae have them, Ranunculaceae do not). In addition, an epicalyx (if present) is diagnostic of subf. Rosoideae, and the seeds of Rosaceae lack endosperm, while those of Ranunculaceae have abundant endosperm.

 

 

 

 

ROSACEAE

Herbs, shrubs or trees with alternate, stipulate leaves; Flowers regular, with 1-many pistils, which are distinct and superior, or united and inferior, and numerous stamens which are inserted on the perigynous calyx; sepals and petal = 5; fruit various

Genera: N.A.-62, IN-21

Crataegus Fragaria Geum Potentilla Prunus Rosa Rubus

Species: N.A.-870, IN-101

Trees, shrubs and herbs

Leaves alternate (very rarely opposite)

Stipules usually present (exception:Spiraeodieae)

* Hypanthium usually conspicuous

Stamens numerous

Fruit extremely variable (follicle, capsule, achene, drupe, pome)

Usually no endosperm.

The subfamilies of the Rosaceae are sufficiently distinct to be worth learning. The distinguishing characteristics of the four largest subfamilies are listed below.

Spiraeoideae

Usually no stipules

Gynoecium apocarpous, superior, of 2-5 carpels

fruit a follicle or capsule

Spiraea

Rosoideae

** Epicalyx often present (sepal-like structures of uncertain origin alternating with the sepals)

Gynoecium apocarpous, superior,of more than 5 carpels

Fruit an achene or drupelet (often dry)

Rubus Fragaria Potentilla Geum Rosa

Prunoideae

Gynoecium superior, monocarpous (1 carpel)

Fruit a drupe

Prunus

Maloideae

Gynoecium inferior, syncarpous, of 2-5 carpels

** Fruit a pome

Pyrus, Malus Sorbus

 

 

 

 

 

Fabales

 

FABACEAE

The legume (pea pod) fruit; all members of this family have this fruit type and it is not found in any other family; trees shrubs or herbs; leaves pinnately or palmately compound or simple; 3 flower types = Papilionaceous (pea flower), Mimosoid and Caesalpinaceous

Genera: N.A.-142, IN-32

Species: N.A.-1521, IN-93

Herbs, shrubs and trees

* Leaves usually pinnately compound with entire leaflets

Stipules present

* Roots form nitrogen-fixing nodules containing Rizobium bacteria

Inflorescence usually a raceme

Perianth of 5 fused sepals and 5 petals

Gynoecium monocarpous

* Fruit usually a legume

The three subfamilies of the Fabaceae are highly distinctive and often treated as separate families. There characteristics are as follows:

Mimosoideae

Flowers actinomorphic

Stamens 10 or more

Caesalpinioideae

Flowers zygomorphic

Upper petal (banner) innermost in bud

Petals all free

Stamens 10 or fewer

Faboideae

Flowers zygomorphic

Upper petal (banner) outermost in bud, enclosing other petals

Two lower petals (forming keel) often fused

Stamens 10

 

 

 

 

Myrtales

 

ONAGRACEAE

Herbs; flowers 4-merous, perfect and symmetrical; 2 or 4-celled inferior ovary, and 4 or 8 stamens; fruit a capsule; hypanthium present, and on its rim ar inserted sepal, petals and stamens

Genera: N.A.-13, IN-6

Epilobium Gaura Ludwigia Oenothera

Species: N.A.-252, IN-30

Mostly herbs

Leaves alternate or opposite, simple

* Usually 4 sepals, 4 petals, 4 or 8 stamens, 4 carpels

* Hypanthium usually extends above the inferior ovary

Pollen joined by sticky threads

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Cornales

CORNACEAE

Trees and shrubs; leaves opposite or alternate, veins curved; flowers 4- to 5- merous; stamens alternate with the petals; ovary inferior; fruit a drupe or berry.

Genera: N.A.- 1, IN-1

Cornus

Species: N.A.- 14, IN-9

Inflorescence usually a corymb or umbel

* Inferior ovary

Usually 2 carpels

 

Euphorbales

 

 

EUPHORBIACEAE

Milky sap; leaves usually alternate;unisexual flowers with staminate flowers surrounding the pistillate;trilocular ovaries; some with no petals, but with glandular appendages; fruit a schizocarp or capsule

 

Genera: N.A.-47, IN-8

Acalypha Chamaesyce Croton Euphorbia Poinsettia

Species: N.A.-358, IN-27

Trees, shrubs and herbs

Leaves alternate or opposite, simple

* Milky juice often present

* Flowers always unisexual

Calyx and corolla often lacking or highly reduced

* Pistil 3-carpellate with 3 styles, each often 2-branched

** Fruit a 3-lobed schizocarp in which the mericarps themselves dehisce after separating

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Rhamnales

VITACEAE

Woody, climbing by tendrils; inflorescences opposite the leaves; stamens opposite the petals; fruit a berry.

Genera: N.A.-4, IN-3

Ampelopsis Parthenocissus Vitis

Species: N.A.-40, IN-10

* Usually woody vines with tendrils (occasionally shrubs or trees)

Leaves alternate, simple or compound

Leaves often with translucent dots

** Inflorescences and tendrils arising opposite a leaf

* Stamens as many as petals and opposite them

Fruit a berry

 

Sapindales

 

 

ACERACEAE

Trees or shrubs; leaves opposite, usually simple with palmate venation; flowers actinomorphic; fruit a winged schizocarp;

Genera: N.A.-1, IN-1

Acer

Species: N.A.-19, IN-6

Trees and shrubs

* Leaves opposite, usually palmately lobed (rarely compound)

Flowers usually unisexual

* Gynoecium biloculate and compressed at right angles to septum

** Fruit a samaroid schizocarp

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Geraniales

 

GERANIACEAE

Flowers 5-merous; stamens with filaments united at base; fruit with elastic schizocarps that curl on the beak

Genera: N.A.-3, IN-2

Erodium Geranium

Species: N.A.-62, IN-7

Mostly herbs

Leaves alternate or opposite, deeply lobed or compound

Gynoecium of 5 carpels fused around a central axis "ovarian beak"

** Fruit a schizocarp breaking up into as many mericarps as there are carpels, the mericarps recurving elastically but held together by the upper part of the ovarian beak

 

 

 

 

 

 

 

 

 

 

 

 

 

Apiales

APIACEAE

Aromatic herbs with hollow stems; Leaves alternate, compound with sheathing base; Flowers in an umbel; flowers 5-merous, often yellow or white; stamens 5 ovary 2-carpellate, bilocular, inferior; plants herbs; fruit a schizocarp

Genera: N.A.-83, IN-28

Angelica Daucus Chaerophyllum Osmorhiza Sanicula Thaspium Zizia

Species: N.A.-391, IN-37

Inflorescence usually an umbel (Sanicula head)

** Styles often swollen at base, nectariferous (the "Stylopodium")