Display variant title on cart page only for items with more than one variant
If you are using separate product types - some with variants, some without:  

Then what you're looking for is basically:

{% for lineItem in cart.lineItems %}
    {% if lineItem.purchasable.product.type.hasVariants %}
       {# the purchasable is the chosen variant - display the product AND variant title #}
       {{ lineItem.purchasable.product.title }} &lt;br&gt;
       {{ lineItem.purchasable.title }}
    {% else %} 
        {# no variants, just use the title from the product #}
        {{ lineItem.purchasable.product.title }}
    {% endif %}
{% endfor %}


If you're using just one product type, some entries of which have one variant and others more:

Basically you need to get back from the lineItem to the product so that would be something like this:

{% if lineItem.purchasable.product.variants|length &gt; 1 %}
    {{ lineItem.purchasable.title }}
{% else %}
    {{ lineItem.purchasble.product.title }}
{% endif %}


...
(I've not tested these directly, just coded here in the browser but that should be pretty 
close!)