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Pass the sweet potatoes. Or is it pass the yams? We often use these names interchangeably, but in reality, they are two very different plants. So, what is the difference between sweet potatoes and yams?
True yams are monocots (like grasses and lilies) in the family Dioscoreaceae that are native to Africa and Asia. Sweet potatoes are dicots that are native to Central and South America and are part of the morning glory family (Convolvulaceae). Additionally, sweet potatoes are not related to potatoes (also called Irish or white potatoes) either, which belong to the nightshade family (Solanaceae) along with tomatoes, peppers, and eggplants.
Yams belong to the
genus Dioscorea, which contains over 600 species of
plants, most of which are tropical. Several different species of yams
are cultivated, with the most commonly grown being white yam
(Dioscorea rotundata) from Africa and water yam (Dioscorea
alata) from Asia. A majority of yam production takes place in
Africa (95% of global production), with Nigeria being the largest
producer. Yams that are available in the United States are typically
grown in Caribbean countries.
Yams grow as a vine and
produce an underground tuber, which vaguely resembles sweet potatoes,
that are long cylindrical. Yams can range in size from the size of a
potato to extremely large, up to five feet long and weighing over 100
pounds! Their flesh can be white to bright yellow to purple or pink,
and the tuber is covered in a tough, scaly skin that is difficult to
remove. They are often boiled and mashed as well as fried, roasted,
or baked (like baked potatoes). Yams are starchier and drier when
compared to the sweet potato varieties most commonly grown in the
Sweet potatoes (Ipomoea
batatas) produce storage roots that have smooth thin skin that
can range in color from white to yellow, red, purple, or brown. These
roots are short and blocky and have tapered ends. The flesh also
ranges in color from white to yellow, orange, or orange-red. Sweet
potato varieties are classified as either ‘firm’ or ‘soft’.
When cooked, ‘firm’ sweet potatoes remain firm and are dry and
crumbly (like a ‘regular’ potato), while ‘soft’ varieties
become soft, moist, and sweet. ‘Soft’ types typically have dark
orange skin, orange flesh. In the United States, these are the sweet
potatoes we usually refer to as yams are (they are also the most
commonly grown sweet potatoes).
So why do we sometimes
call sweet potatoes yams? According to the Library of Congress, the
confusion between yams and sweet potatoes began when soft varieties
of sweet potato were introduced to the United States: “In the
United States, firm varieties of sweet potatoes were produced before
soft varieties. When soft varieties were first grown commercially,
there was a need to differentiate between the two. African slaves had
already been calling the ‘soft’ sweet potatoes ‘yams’ because
they resembled the yams in Africa. Thus, ‘soft’ sweet potatoes
were referred to as ‘yams’ to distinguish them from the ‘firm’
Today the USDA requires
that when the term ‘yam’ is used to describe sweet potatoes, it
must also be labeled as a ‘sweet potato.’ Unless you specifically
search for yams, which can often be found at ethnic markets, you are
probably eating sweet potatoes.
with this knowledge, you now have a great conversation starter for
the Thanksgiving table. Or, if your family is anything like mine,
they’ll roll their eyes and grumble here they go again.
Good Growing Fact
of the Week: In addition to requiring warm moist
conditions for growth, edible yams also have a very long time to
harvest. Plants often require 6-12 months of growth before their
tubers can be harvested. Sweet potatoes, on the other hand, typically
take around 100 days to harvest.