Last year I had the pleasure to participate in the Van Cortlandt Park BioBlitz along side Richard Abbott, a wonderful botanist from the New York Botanical Garden. During his introduction to the students, he spoke about two different ways to approach plant identification. He called the first "imprinting". You learn the identification of plants by some means - someone tells you what it is or perhaps you look it up in a field guide. You learn that species. You do the same for each species you meet. This is how I started learning plant ID. It works, but there is a much better way. He explained the benefits of the second method - learning the characteristics of plant families. If you learn one plant at a time (the imprinting method), each time you go into the field and meet a new plant, you have no foundation from where to begin your identification process. If you learn characteristics of families, you can immediately start narrowing down your choices and arrive at an identification much more quickly. For the next few blog entries, I thought I would begin sharing with you some family characteristics, focusing on species Daniel and I have collected for the project.
Today, let's start with the mustards, Brassicaceae. Many mustards bloom in the early spring, with some of them continuing through spring and summer. Brassicaceae is the family from which we get not only mustard, but a whole group of vegetables including cabbage, broccoli, cauliflower, brussels sprouts, kale, turnips and canola oil. But today we are focusing on the species you find growing wild in Central Park.
This family is made up of mostly herbaceous species. The few woody species that exist are not from this part of the world. These herbaceous plants are often weedy, living in disturbed areas. It is also a family that is mostly found in the temperate and colder zones of the Northern Hemisphere, with very few species in the tropics.
The flowers are generally four-petaled, have four sepals, six stamens (four tall and two short) and one pistil with two stigmas. The four petals are often in the shape of a cross which gives us the old family name, Cruciferae (cross-bearing). The flowers are small but found in inflorescences, some of which can be quite showy. They are usually terminal, that is, found at the end of the stem.
The fruit, a silique, is a dry seed pod that is divided into two chambers by a papery partition and the pod splits open on two sides. The pods come in different shapes and sizes. Whatever shape they are, they spiral around the stem. When the mature pods split open, there are generally two rows of seeds in each partition.
The leaves in this family are usually alternate, sometimes in a basal rosette (leaves in a circular arrangement close to the ground). The leaves usually have an odor when they are crushed. These odors come from "mustard oils", compounds that contain sulfur. They taste bitter but are usually not poisonous.
Many of these species are host plants for the cabbage white butterfly, that is, they are the food plant for the caterpillar of this species of butterfly. They also provide nectar for a host of other insects.
The first example here is one of the most common species we have. It is a European species that is an invasive in our woodlands. Garlic mustard, Alliaria petiolata has a white, four-petaled flower, typical of the family. It is a biennial that produces seed pods very soon after flowering. It is an easy weed to remove, but if you are trying to get rid of this plant, you must pull it before it begins flowering to avoid spreading the seeds. If you crush the leaves, you will see where it gets its common name - it gives a strong fragrance of garlic.
Arabidopsis thaliana is an annual and is the fruit fly of plant research - it has been used in countless genetic studies and was the first plant to have its entire genome sequenced. It is native to Eurasia and northwestern Africa. The first photo below shows the seeds pods ripening while the stalk is still flowering. In the second photo below, you can see the leaves are in the basal rosette formation, low to the ground with few leaves on the flower stalks. It has a four petaled white flower, much less showy than Alliaria petiolata. It is a considerably less robust-looking plant than garlic mustard!
Another white-flowering mustard with long narrow seed pods is Cardamine hirsuta, hairy bittercress. This Eurasian native continues to flower as seeds ripen and the seed pods ascend past the flowers, almost vertical, as you can see in the second photo below. Its leaves are in the basal rosette formation, but these are pinnately lobed with each leaflet being round with wavy margins. If you look closely at the first photo below (or better yet, at a live sample on one of your walks!), the petioles (leaf stalks) have a few coarse hairs, hence the scientific name of the plant- hirsute means hairy. The main stem is hairy toward the bottom and hairless above.
This next mustard has yellow flowers, Sisymbrium officinale, Hedge mustard. A European native, it is easily recognized by its branching pattern. It is a fairly large plant that branches abundantly, often at right angles to the main stems. In the second photo below you can see the leaves are narrow and lobed. The flowers are small with four yellow petals and four green to yellow sepals. The seed pods are appressed against the stem and curve up at the tips.
Virginia pepperweed (Lepidium virginicum) is an annual that produces flowers and fruit for most of the growing season. Unlike many of the other member of this family that are from Eurasia, it is native to most of North America. The tips of the stems have numerous white flowers and the seed pods can be seen spiraling along the stems. The common name refers to the fact that young leaves and mature seed pods have a peppery taste. The seed pod is round with a shallow notch at the apex. The stems are covered with short, fine, white hairs. This species begins blooming in spring, peaks in summer and can still be found blooming into the fall.
Another Eurasian species, Capsella bursa-pastoris, has seed pods that, to me, look somewhat like little hearts spiraling around the stem. But in fact the scientific and common names refer to a shepherd's purse. This is a very common weed and I have always enjoyed the little fact that the fruits are named for a shepherd's purse, but Daniel recently gave me a bit more information on this topic: shepherds made their purses from sheep scrotums! I will leave you with that fun fact and move on to our next species!
Whitlow grass (Draba verna) is a tiny beauty that can be found in lawns, roadsides and other disturbed areas. A native of Eurasia, it has naturalized over North America. The seed pods are somewhat oblong and the leaves form a basal rosette. You have to squat close to the ground to appreciate this one, but it is worth it.
For our last species of this blog, let's look at a very showy plant. Lunaria annua not only has bright violet inflorescences, it has large interesting seed pods. The seed pods are oval (or moon-shaped, which is what lunaria means) and translucent, you can see the seeds inside. Some of the common names such as Money plant or Silver dollar plant refer to the fact that the seed pods look like silver coins. These are often used in flower arrangements. The species is from Europe but has naturalized in many areas. In Central Park, Daniel and I know this species from one area only, in the Ramble by the Still Hunt statue on the east drive. If you find any in another part of the park, be sure to let us know!