Brassicaceae: Mustard Family — Cress

Members of the mustard family all have four petals, usually in a cross shape (hence Cruciferae; the old name for the family).  With some groups, the flowers are quite similar, so it helps to pay close attention to the fruits.  This is especially true for the mustards themselves (Brassica, Hirschfeldia, Sisymbrium, Caulanthus and Turritis).

Fruits in the Mustard family are of two kinds, siliques and silicles.  Siliques are at least twice as long as they are wide, while silicles are less elongated.  Some siliques are more or less cylindric, others (as in the Wild Radish) are noticeably fatter at the base and taper towards the tip.  Some silicles are erect and appressed to the stem, others grow outwards and curve upwards, or outwards and curve downwards.

Mouse-ear / Thale Cress – Arabidopsis thaliana

Blooms:

Feb–May

Plant Height:

6–30 cm

Flower Size:

Very small

Origin:

Eurasia

Habitat:

Disturbed ground, sandy areas, flats, fields

Notes:

An uncommon cress, found on Fort Ord.  It has diminutive white flowers with 6 stamens and 4 petals.  Fruits are spreading to ascending, cylindric siliques, 1–5 cm long, hairless and unsegmented, borne on  distinct pedicels. It has a well-formed basal rosette of hairy leaves.

American Winter Cress – Barbarea orthoceras

Blooms:

Mar–July

Plant Height:

20–60 cm

Flower Size:

Small

Origin:

Native

Habitat:

Moist places, usually above 700 m

Notes:

Closely related to the mustards, but the glabrous leaves and the pinnately lobed leaves subtending the flower heads are distinctive, as is the vivid green coloring. There is also a basal rosette of leaves, each with 2–4 pairs of lobes.

Milkmaids / California Toothwort – Cardamine californica

Blooms:

Jan–May

Plant Height:

27–70 cm

Flower Size:

Medium

Origin:

Native

Habitat:

Shaded sites, woodland

Notes:

One of the most common shade-loving plants blooming in early spring.  It has loose clusters of pure white (occasionally pink-tinged) 4-petalled flowers on distinct pedicels.  Leaves have 3–5 leaflets of varying shapes, from narrow to arrow-shaped though broad to rounded, sometimes with small but distinct lobes.

Hairy Bitter-cress – Cardamine hirsuta

Blooms:

Feb–July

Plant Height:

10–35 cm

Flower Size:

Very small

Origin:

European

Habitat:

Shaded sites, woodland

Notes:

This is a common weed with tiny white flowers.  The petioles of its leaves have hairy margins.  The basal leaves are round to kidney-shaped (see right photo), with cauline leaves smaller and sometimes narrower.  It is similar to Western Bitter-cress (Cardamine oligosperma), but most easily distinguished by a close examination with a hand lens.   Western Bitter-cress is not illustrated here, but it lacks the petiole hairs.  Also, Hairy has 4 (occasionally 6) stamens, while Western consistently has 6.

 Heart-podded Hoary Cress / Whitetop – Lepidium draba

Blooms:

Apr–Aug

Plant Height:

20–65 cm

Flower Size:

Medium cluster

Origin:

Europe

Habitat:

Disturbed areas, pastures, fields

Notes:

The plant has a stout, erect, branched stem.  Cauline leaves are 3–9 cm long, ovate to obovate and widely spaced.  The inflorescence is slightly domed, with individual flowers on pedicels of varying lengths.  Petals are white, clawed and 2 x sepal length.  Fruits are flat, heart- to kidney-shaped, the top neither winged nor notched.

Watercress – Nasturtium officinale

Blooms:

Mar–Nov

Plant Height:

10–110 cm

Flower Size:

Small

Origin:

Europe

Habitat:

Streams, springs, marshes, lake margins

Notes:

This is commonly found in or by streams in sometimes dense mats, with small clusters of white flowers.  Stems can be long, but are weak and mostly prostrate, rooting at nodes.  Leaves are pinnately parted, with 3–9 round to lanceolate leaflets, which have a peppery taste. Fruits are cylindric siliques, straight or up-curved and narrowed between individual seeds.

Western Yellow Cress – Rorippa curvisiliqua

Blooms:

Mar–Sept

Plant Height:

10–40 cm

Flower Size:

Medium cluster

Origin:

Native

Habitat:

Streambanks, seeps, mud flats

Notes:

Much branched from its base. The basal leaves are not rosetted and are noticeably toothed.  Cauline leaves are pinnately lobed. The inflorescence is elongated. The conspicuously upturned siliques are distinctive, giving the species its scientific name.

Shepherd’s Cress – Teesdalia nudicaulis

Blooms:

Feb–May

Plant Height:

5–15 cm

Flower Size:

Very small

Origin:

Europe

Habitat:

Disturbed areas

Notes:

An uncommon cress, to be found on Fort Ord.  Like Mouse-ear Cress (Arabidopsis thaliana, see above), it has diminutive white flowers clustered at the stem tips, each with 6 stamens and 4 unequal petals.  The fruit is a silicle (quite different from the siliques found on Mouse-ear Cress), heart-shaped to round with a shallow notch at the tip.  There are two seeds in each chamber (an important diagnostic feature).  Leaves are in a well-formed basal rosette, glabrous and entire or irregularly lobed.