Pennycress is native to the temperate regions of Eurasia, in many of which it is an archaeophyte (an ancient introduction). It has been naturalized to North America. Although the white flowers are kind of pretty, this is one "wildflower" that I will fully agree is a weed that you don't want in your yard. However, I found it in our yard. We live on acreage, and all kinds of things will pop up.

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Name: Field Pennycress (Fanweed, Stinkweed)
Scientific Name: Thlaspi arvense L.
Plant Family: Mustard (Brassicaceae)
Prime Season: Spring to Early Summer Flowering

Field Pennycress is an introduced erect annual forb growing from 4 to 20+ inches high on hairless flowering stems, without branching or only a very little near the top. Plants that germinate from seed in the late summer will form a winter rosette and the flowering stem the next spring. Stems are ribbed and sometimes with small wings.

The leaves are of two types. Basal leaves are oblanceolate, that is, taper to a pointed base resembling a stalk, are longer than wide and broadest above the middle. The blade is oblong with some marginal wavy indentations or entire and the tip is rounded. Stem leaves are oblong, stalkless and clasping with an auricled base. These auricles have a blunt point at the base. Upper leaves have margins with coarse rounded to pointed teeth. The basal leaves drop away early.

The inflorescence is a cluster (a raceme) of stalked flower buds, somewhat flat-topped, that occurs at the top of the main stem and any side stems rising from the leaf axils. As flowers open, the cluster elongates.

The flowers are 4-parted with a calyx of 4 green sepals and the corolla has 4 white petals that are 2x as long as the sepals and narrow to a claw-like base. Each flower is only 1/8 inch wide blooming first from the lower section of the raceme, which then elongates as more flowers come into bloom and older flowers produce seed. Flowers are held by short stalks that up curve slightly. The stamens are slightly tetradynamous, that is, in two sets, 4 around the greenish pistil and two shorter lateral stamens that have a pair of nectar glands at their base. This is typical in the Mustard family. Anthers are yellow; the pistil has a blunt flattened tip to the stigma.

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Here is an article from the University of Missouri: https://ipm.missouri.edu/cropPest/2016/4/Weed_of_the_Month-Field_Pennycress/